Another silly power question

[mikeosoft]

Hi everyone,
The venues in which I am asked to go have camlock and/or Nema 14-50 240V. The question is for those venues that are having only Nema power.
I have one distro which is 200A single phase 120V camlock.

My question is... if I have 2 different sources of 50A 240V, is it possible to wire my 200A panel with 2x Nema 14-50 to be able to use my panel at full capacity?
Some sort of parallel wiring: My panel has 4 camlock wires and each wire would go to an end of the Nema plug to gain 50A per hot lug so would give me 100A per Nema?

I wish I could understand more what is doable and what is not!
Anyway, Thank you! and don't worry, all this (if at all possible) will be made by a professionnal.

[iLightTheStage]

Simple answer: No.

THE FOLLOWING IS GENERIC INFORMATION AND THEORY, NOT INTENDED TO GUIDE OR INSTRUCT THE USE OF ELECTRICAL WIRING.

Firstly, NEMA (National Electrical Manufacturers Association) creates standards for connectors and other electrical devices. It basically means that a NEMA connector has to meet certain guidelines.

When you have the option, always tie in with the camlok power supplies. They most likely (but no guarantee) will have more available power. The venue should be able to tell you how many Amps the service has. THAT is your limit. Even though your rack has the capacity to hook up 200amps, if the power service it is connected to is only, say, 100amps, that is your limit.
Simply: think of the wiring in your house. You have a circuit breaker in your panel that says "15amps". Now, in THEORY, you could wire up 100 outlets to this breaker. But it doesn't matter how many outlets you have, it is still limited at 15amps. Trying to replace that to a 20amp without electrical knowledge is dangerous and stupid. That breaker is that size for many reasons I'm not going to get into, but on the simplest level: it's to TRY to HELP prevent your house from having an electrical fire.

So, you have to know how much you are plugging into your rack, and how much power is available to your rack from the service.

DO NOT make some device to pull power from two different 14-50 outlets and combine it into your rack. This is HIGH VOLTAGE. This is deadly. You do not want to mess with it. And I doubt you could get any "professional" to build you such a device. At least, not someone who should be called a professional. I'm not going to get into the details of it, that is not allowed here, and sometimes only a little knowledge can be even more dangerous. You have to know your electrical limits and stay within them.

I'm not saying this to be a jerk, but to stress how NOT advisable doing something like that is. Regardless of the fact of whether or not you can physically create such a beast. It is good that you asked and didn't just "do", which is sometimes all it takes for people to get killed.

[church]

If I understand your question correctly you want to use two stove plug outlets to feed a single distro, effectively connecting both stove outlets in parallel. This is forbiden by all the Provincial and Canadian codes. If attempted it is extremely dangerous for multiple reasons which I shall not go into but you risk destruction of the equipment, damage to the building supply equipment, electrocution to yourself or who ever makes the connection and causing a fire.

The only way you can safely use multiple stove outlets is with multiple fully isolated distros.

[STEVETERRY]

Hi everyone,
The venues in which I am asked to go have camlock and/or Nema 14-50 240V. The question is for those venues that are having only Nema power.
I have one distro which is 200A single phase 120V camlock.

My question is... if I have 2 different sources of 50A 240V, is it possible to wire my 200A panel with 2x Nema 14-50 to be able to use my panel at full capacity?
Some sort of parallel wiring: My panel has 4 camlock wires and each wire would go to an end of the Nema plug to gain 50A per hot lug so would give me 100A per Nema?

I wish I could understand more what is doable and what is not!
Anyway, Thank you! and don't worry, all this (if at all possible) will be made by a professionnal.

Short answer: NO
Long answer: Definitively NO

ST

[tk2k]

Okay now that we've established there's no way in hell OP should do this, someoen wanna give him some information about why the parallel wiring is so dangerous?

[SteveB]

Besides being against all kinds of applicable codes for the OP's application, it should be noted that parallel wiring is commonly used for main feeder wires, where multiple set's of 500MCM or such wiring is used to bring power into a building from the utility source, in order to get the building service at it's required capacity. In these instances, great care is taken to make sure the wires feeding a phase are exactly the the length (or near enough) so as to eliminate a higher current draw on a set of wires due to shorter cable length. This (to my knowledge) is the only allowed use of multiple feeders.

In the OP's instance, there is no guarantee that the main feed wires you tap to parallel feed will come from the same phase initially. Big explosion results if you guess wrong.

[n1ist]

That and the risk of having a live male cord cap in your hand...
/mike

[JD]

One other thing (Kind of covered by SteveB above) is that unless the paths are of exactly the same resistance, the majority of the power will come in via the lower resistance path. You may say, "Well, there are breakers that would interrupt it" but that is not true on the neutral. So in summary:
Phase miss-match = Boom!
Resistance miss-match = Fire!
Switch/Breaker Back-feed = Electrocution!
Live male connector = Boom, Fire, and Electrocution!

[church]

two other items to consider:

1) the phasing: the split circuit feeding a stove outlet assumes both legs are offset in phase by 180 degrees. it is not critical which leg has the red conductor and which side has the black conductor in normal use. However if two 120/240 split supplies were to be connected in parallel then the phasing is critical and the phasing of the legs must be known to prevent a problem. The colour coding of the wiring can not be relied on. When multiple supplies are connected to a power distribution bus this is a permament connection where this information is known.

2) if two stove plugs are attached in parallel to the distro and one is connected to the supply through a stove outlet the neutral and the two live connectors on the second stove plug are also live but exposed and someone may be electrocuted by coming in contact with the plug. I know it is possible to build in isolation switches to prevent this but it requires a lock out/tag out procedure to ensure this is done and is against code. Unfortunately whoever approved this procedure is liable for this and here in Ontario and I assume the other provinces and the OP is in Quebec this would definitely require a Professional Engineer to approve it - good luck getting that approval. I for one would definitely not approve it.

[STEVETERRY]

two other items to consider:

1) the phasing: the split circuit feeding a stove outlet assumes both legs are offset in phase by 180 degrees. it is not critical which leg has the red conductor and which side has the black conductor in normal use. However if two 120/240 split supplies were to be connected in parallel then the phasing is critical and the phasing of the legs must be known to prevent a problem. The colour coding of the wiring can not be relied on. When multiple supplies are connected to a power distribution bus this is a permament connection where this information is known.

2) if two stove plugs are attached in parallel to the distro and one is connected to the supply through a stove outlet the neutral and the two live connectors on the second stove plug are also live but exposed and someone may be electrocuted by coming in contact with the plug. I know it is possible to build in isolation switches to prevent this but it requires a lock out/tag out procedure to ensure this is done and is against code. Unfortunately whoever approved this procedure is liable for this and here in Ontario and I assume the other provinces and the OP is in Quebec this would definitely require a Professional Engineer to approve it - good luck getting that approval. I for one would definitely not approve it.

There is no possibility that this dangerous and non-compliant installation would be:
A. Installed by a licensed contractor
B. Approved by any licensed engineer or AHJ

Not to sound testy, but I suggest we refrain from dreaming up improbable situations where A. or B. might happen--because they ain't gonna.

/soapbox ON/

Sometimes the correct answer to an uniformed poster is simply NO.

I would like to see more technicians in the entertainment industry actually reading the NEC or the CEC depending on their location. The "why" of the "NO" is clearly outlined in each of those very handy documents. They should be in every electrician's toolbox. And, if any CB members are contemplating an ETCP certification, they will need to know the rules surrounding a hypothetical situation such as the one posed by the OP.

/soapbox OFF/


ST

[derekleffew]

While I agree that every technician should become more familiar with local and national codes, I disagree with the following:

... /soapbox ON/
...The "why" of the "NO" is clearly outlined in each of those very handy documents. ...
/soapbox OFF/

Hmm, let me think...
* Double neutral on a dimmer rack,
* "Extra" breaker on a road show connection panel,
* Use of SJO in break-out assemblies and adapters,
are but three of the topics about which you've had to explain here, and on multiple occasions. If the "why" of the "no" was so clearly defined, further explanation wouldn't be necessary, now would it?
Or are you calling us all stupid because we can't always glean the original intent of the code writers of some seemingly arbitrary rules?
When I hear that, it makes me want to throw up a little.

[church]

There is no possibility that this dangerous and non-compliant installation would be:
A. Installed by a licensed contractor
B. Approved by any licensed engineer or AHJ

Not to sound testy, but I suggest we refrain from dreaming up improbable situations where A. or B. might happen--because they ain't gonna.

ST

Unfortunately I have seen more than one dangerous installation performed by licensed contractors and not just in the theatre: the engineers or AHJ are also not perfect - everyone has an error rate. Personally I try not to make assumptions. The original question posted by the OP could be done without any licenced contractors. Strange as it seems I was asked this question five years ago.

In principle a simple NO should suffice but is "No" a good answer? If we are unable to support the "No" with an explanation then the person who asked the question in the first place still does not know why they should not implement their idea and may then go and ask someone else who is equally unknowlegable but says "yeah should be okay" and proceeds with the second advice - after all they received the same supporting data for the answer so from their perspective it is just as good.

The Canadian and Ontario Electrical Code are not written to provide technical instruction - it provides the rules. The reasoning behind the rules requires explanation after all there is a reason for all the courses that are provided to teach electricians and others how to use these codes and the rationale behind them.

This and other similar forums will cease to exist if the answers to posted questions become: "no", "yes", "read the code", "read the manual" etc. I know this is not what ST meant to imply by his post

[STEVETERRY]

While I agree that every technician should become more familiar with local and national codes, I disagree with the following:

Hmm, let me think...
* Double neutral on a dimmer rack,
* "Extra" breaker on a road show connection panel,
* Use of SJO in break-out assemblies and adapters,
are but three of the topics about which you've had to explain here, and on multiple occasions. If the "why" of the "no" was so clearly defined, further explanation wouldn't be necessary, now would it?
Or are you calling us all stupid because we can't always glean the original intent of the code writers of some seemingly arbitrary rules?
When I hear that, it makes me want to throw up a little.

Nobody is calling anyone stupid. And I'm willing to go on explaining all day long, which I'm sure you well know from my articles and posts. My gripe is with those people who work with electrical equipment in our industry, but who feel the NEC is a document that has no value or is too complex, so they don't even look at it!

BTW, there isn't much that's "arbitrary" in the Code--there's a technical reason for almost every rule.

ST

[STEVETERRY]

Unfortunately I have seen more than one dangerous installation performed by licensed contractors and not just in the theatre: the engineers or AHJ are also not perfect - everyone has an error rate. Personally I try not to make assumptions. The original question posted by the OP could be done without any licenced contractors. Strange as it seems I was asked this question five years ago.

In principle a simple NO should suffice but is "No" a good answer? If we are unable to support the "No" with an explanation then the person who asked the question in the first place still does not know why they should not implement their idea and may then go and ask someone else who is equally unknowlegable but says "yeah should be okay" and proceeds with the second advice - after all they received the same supporting data for the answer so from their perspective it is just as good.

The Canadian and Ontario Electrical Code are not written to provide technical instruction - it provides the rules. The reasoning behind the rules requires explanation after all there is a reason for all the courses that are provided to teach electricians and others how to use these codes and the rationale behind them.

This and other similar forums will cease to exist if the answers to posted questions become: "no", "yes", "read the code", "read the manual" etc. I know this is not what ST meant to imply by his post

All good points!

ST

[mikeosoft]

First of all, thank you for all the informations you gave me. It's very informative and I was clearly not aware of all these dangers.
I think I just recalled myself at 8yo doing some projects with DC batteries and thought "Hey, what about adding another battery to get more power!". Those AC principles are never been teached to me and I think everyone should have a REAL class at high school about that. But I'm glad you guys are there to get out these nasty thoughts out of me hehe!

[shiben]

BTW, there isn't much that's "arbitrary" in the Code--there's a technical reason for almost every rule.

Perhaps it would be useful to have some form of document that would explain the "why" bits of these things, perhaps for one not possessing EE training? It would help to clarify the SEEMINGLY arbitrary things...

[STEVETERRY]

Perhaps it would be useful to have some form of document that would explain the "why" bits of these things, perhaps for one not possessing EE training? It would help to clarify the SEEMINGLY arbitrary things...

And there is just such a document! It is the NEC "Handbook" published by the NFPA. In it, every section of the Code is annotated in considerable detail to explain the contents of the section. In most cases, the source of data for the explanation is the substantiation for the proposal that got the section into the Code.

As a sample, here is an example explaining the sections that require oversized neutrals to feed portable switchboards:

Section 520.53(O)(1) involves overlapping concepts regarding the neutral conductor in power supplies for portable switchboards. If a 3-phase, 4-wire switchboard of any kind is brought into a space that has only single-phase, 3-wire service, the switchboard most likely will be connected with two phases to one leg and one phase to the other. This connection could double the current flowing through the neutral, so the neutral must be double size to allow for that possibility. The exception to 520.53(O)(1) provides for a smaller neutral sized for the single-phase feed where a switchboard contains switching devices that can divide the B-phase load equally between the A-phase and C-phase buses for single-phase operation.

Additionally from 520.53(O)(2), 3-phase, 4-wire switchboards that contain solid-state phase-control dimming devices must, when connected to a 3-phase, 4-wire supply, be connected to that supply with a multiconductor cable sized by counting the neutral as a current-carrying conductor or with a set of single-conductor cables where the neutral is sized 130 percent greater than the phases.

Application Example

A 3-phase, 4-wire switchboard containing six 50-ampere SCR dimmers (100 amperes per phase) without a reassignment switching system would have to have a 200-ampere neutral. (A single-phase, 3-wire-only switchboard would not have to meet this special requirement.) This 200 percent rule would cover all the components making up the neutral conductor system inside or permanently attached to the switchboard, to allow for a full-size, single-phase, 3-wire feed when two of the 3-phase, 4-wire phase conductors are terminated to one single-phase, 3-wire leg. Note that the 200 percent neutral already covers the derating requirements (125 percent for a multiconductor feeder system and 130 percent for a single-conductor feeder system) when used in the 3-phase mode. If a reassignment system were added, the neutral would be required to be only 150 amperes. Again, when used in the 3-phase mode, the derating factors would be covered.

The double-neutral requirement covers the terminal and associated busbar or wiring. This requirement begins at the main input terminals or busing, main input inlet connector, or attached main input cord-and-plug set and includes all wiring on the load side of that point.

Power supply feeders easily detached at the terminals or inlet connector need not adhere to the 200 percent neutral rule, because they can easily be sized on a show-by-show basis for the type of supply encountered. These cables must, however, adhere to the requirements of the neutral as a current-carrying conductor or to the requirements of the 130 percent single-conductor-cable neutral.

Solid-state sine-wave dimmers are linear devices that do not add nonlinear loads to the neutral conductor. Where feeders supply solid-state sine-wave dimmers, the neutral conductor is sized by considering it as a non–current-carrying conductor. However, it must have an ampacity of at least 100 percent of the ampacity of the phase conductors.

The Handbook itself is fairly expensive and weights about 10 pounds. 2011 was the first time in many years that I did not buy one. Why? Because the NFPA has a great new web subscription service called "NEC Plus". With it, you get:
--The current Code with Handbook commentary
--The previous Code with Handbook commentary
--The NFPA70E standard for electrical safety in the workplace
--Pertinent links to the UL White Book on applicable Code sections

Plus, it's all searchable. It's a fantastic resource that I highly recommend.

ST

[TimMiller]

The proper way of going about your problem is get a little distro commonly called spider boxes in the construction world. They can be found used on the Internet. Another way I have seen done is they have multiple 50 amp distro panels in a rack then there is a set of cam to whatever nema connection that feeds the multiple distros. Their are also breakers next to each nema split out of the cam panel to prevent a single distro from overloading the cord and connector. The particular setup I am talking about was built by motion labs. They are the rolls Royce of power distribution and motion control for our industry.

[urban79]

Out of complete curiosity, does this apply to lower voltage or amperage plugs? Let's say a 30 amp and 20 amp circuit combined to make 50 amps at 120 volts? I've used one of these before for a motorhome, and I'm curious why some of the issues mentioned above don't apply: 50 Amp Adapter

Chris

[BGW]

That adapter has two hots, a neutral, and a ground. It's not running a paralleled 120vAC 50a circuit- it's running two separate circuits. It just allows for a one-cable hookup to the RV. It's similar to the dimmer packs with two 120vAC input receptacles- those run two separate circuits in one device.

[urban79]

My electrical theory is really rusty!

[ship]

Thus my not being sufficient these days to post on such matters in now educating or refreshing me. Thanks stevetery for the long form version of your reply. You are very vibrant and necessay in this post to all and thanks for doing the long form.


I have the like 1999 version of the handbook as with that version of American Electrician's Handbook which is more extensive.

At some point, you really do have to buy and read cover to cover as best you can if want to be serious about code. No internet skipping around will solve the general stuff that comes up. That if serious about your own doing wiring. Neither are cheap but I would think while really boring especially in many chapters - if you want to become an electrician.. good to buy and try as hard as you can to read the hard cover version of.

As said, once you get the concept, keeping up with code changes stems from something already known about. That's the easy part in even making your own.

[Chris15]

Bluntly, that RV adapter is dangerous.

All it takes is one outlet with an active/ neutral reverse and you have full line voltage exposed on a male connector...

[BGW]

Yeah, I neglected to mention that the two circuits share a neutral. What you say is absolutely true. The dimmer packs that are set up like that isolate the neutrals from each other to prevent that.

[ship]

Yeah, I neglected to mention that the two circuits share a neutral. What you say is absolutely true. The dimmer packs that are set up like that isolate the neutrals from each other to prevent that.

Fascinating, tell more about this isolation technology for a neutral.

[BGW]

Fascinating, tell more about this isolation technology for a neutral.

It's nothing fancy- I wouldn't even call it technology. Maybe more of a wiring method. Usually those packs are 6 channel units. One cord/input (circuit) feeds three channels and the main electronics, and the other is only connected to the remaining three channels and their associated dimmers.

[Chris15]

Let's go slightly generalised for a moment here, I don't know the specifics of the packs in question.

You can broadly break a dimmer down into 2 parts - the control side (generally running at extra low voltage) and the power side running at a somewhat higher voltage.
generally the trigger link between control and power will be an optocupler so inherently you have galvanic isolation between control and power at that point. (We'll ignore for now the sensing circuits neccessary to detect the zero crossings etc.)

Given that galvanic isolation, there is no reason why each power "block" if we can call it that, can't be fed from a different source, because the only copper connections will be mains in and mains (dimmed) out.

So say you have 6 dimmer "blocks" in a pack - then you busbar the actives and neutrals of 3 of them to one incoming supply lead and separately busbar the other 3 to a second supply lead.
Importantly you DO NOT bond the neutrals. You DO bond the Earths though...

[derekleffew]

Bluntly, that RV adapter is dangerous.
All it takes is one outlet with an active/ neutral reverse and you have full line voltage exposed on a male connector...

I don't see the problem. It says right there on the page

Polarity check of each park receptacle is recommended before use

We've discussed semi-similar devices here and here, but neither Mr. Terry nor anyone else, has cited the section where the device is forbidden in the NEC.

[Chris15]

I don't see the problem.

Hang on, you don't see the problem with trailer owners needing to perform an optional test?
What's more one that requires the purchase of additional equipment...

Not for use with GFI receptacles.

Warning bells at 200 metres

So if for a moment we neglect the option of a miswired outlet, how about the usage case where only one plug is in use but is drawing a full 30 amps.
There will be a few volts voltage drop across the neutral conductor meaning that exposed neutral pin will NOT be at 0v. Enough voltage to cause serious injury under normal circumstances - probably not, but a risk none the less. Add damp conditions around it (not unexpected in a caravan park) though and things could really get fun...

This is no different than any other shared neutral situation where linked breakers are required. The plug/s and socket/s are effectively a breaker and thus must be linked...
Just don't try and prove the connection between that and the code

[STEVETERRY]

I don't see the problem. It says right there on the page


We've discussed semi-similar devices here and here, but neither Mr. Terry nor anyone else, has cited the section where the device is forbidden in the NEC.

Ahem....

406.7 Attachment Plugs, Cord Connectors, and Flanged Surface Devices.

(B) Connection of Attachment Plugs. Attachment plugs shall be installed so that their prongs, blades, or pins are not energized unless inserted into an energized receptacle or cord connectors. No receptacle shall be installed so as to require the insertion of an energized attachment plug as its source of supply.


The requirements in 406.7(B) were originally found in product information only. However, as an aid to the inspection community, these requirements are now clearly stated in the NEC. A live attachment plug cap can be a dangerous situation. Attachment plug caps should never be installed so as to allow the blades to be energized without being plugged into a device.

ST

[STEVETERRY]

Bluntly, that RV adapter is dangerous.

All it takes is one outlet with an active/ neutral reverse and you have full line voltage exposed on a male connector...

Right! It also violates NEC section 406.7(B).
ST

[TimMiller]

I believe that on the second plug just the hot is connected so you do not have the problem of a hot neutral.

[BGW]

I believe that on the second plug just the hot is connected so you do not have the problem of a hot neutral.

But then if the two breakers the device is pulling from are on the same leg, you'd have a severely overloaded neutral. Not to mention the high potential for a length mismatch between the hot and neutral conductors...

[JD]

It's nothing fancy- I wouldn't even call it technology. Maybe more of a wiring method. Usually those packs are 6 channel units. One cord/input (circuit) feeds three channels and the main electronics, and the other is only connected to the remaining three channels and their associated dimmers.

Well, yes and no. Each AC input must have it's own step-down transformer to the control circuit. That way, the zero-voltage cross detector for the dimmers maintains phase relationship with the incoming power for those dimmers. Otherwise, if the second AC input was plugged into a receptacle on a different phase leg, the trigger circuit would be firing at the wrong time.

[TimMiller]

But then if the two breakers the device is pulling from are on the same leg, you'd have a severely overloaded neutral. Not to mention the high potential for a length mismatch between the hot and neutral conductors...

I guess then it is possible to overload the neutral but your 220v devices would not work because they will see 0v. I need to find one of my rv books and see what solutions they have.