Urgent Electrical Question

[jstroming]

Doing an event right now at a well-known convention center, and venue electrician has siamesed 2x 100Amp 3phase boxes (about 150ft away from each other) to give us 1x 200Amp service. I have calls in to electrician friends but it's getting late on a Saturday.....just want to know how stupid/dangerous this is or isn't....

He's also using a cam tee on a neutral for a few extra inches and left the 2nd male contact exposed about 4ft off the ground (this is a children's event). I electrical taped off in a pinch before doors. Again unsure of risk here.

Thanks for replies this late.

 

[JD]

Would make the hair on my back stand for a long list of reasons! A reversed leg would make for one heck of a bang in one of those boxes! Bottom line is if he is the venue electrician (and has probably done this in the past) then you can either differ authority to him or walk. The exposed conductor is something I would complain about. Even if everything else is connected up right, running paralleled OCPDs is bad news. (we won't even talk about the code violations) You may not have 200 per leg as the flow will take the path of least resistance so the draw will favor the box that is closest. Given everything else, make sure you meter what he has given you before powering everything up.

 

[jstroming]

Yeah I'm used to doing shows in Central America so nothing surprises me, I wouldn't walk from a show anyway since I work directly for producer.

Lighting guy mentioned more of a pull on one box, but we're running closer to 100A anyway so that shouldn't be too big of a concern.

We metered 119-121 between all legs and neutral.

 

[jstroming]

Here is a pic of breaker (it's one of those portable type jobs). Notice exposed neutral.

 

[Dionysus]

As an electrician, that is very wrong and against code for a reason. Honestly if I saw that I would contact the AHJ without a doubt. take lots of photos and send them off.
If need be, do the show and keep an eye on it (Id want to keep draw as close to under 100A per leg as possible) but really that is not right. Really you should just use the feeds separately instead of trying to parallel them.
And yes the neutral may be a 'grounded conductor' but it should not be left exposed like that!

It sucks kicking the hornets nest, but we have electrical codes for a reason.

 

[lwinters630]

To me it's not a matter of keeping the load under 100, what if a short happens. It will pass thru the 200 and may not trip the 100 timely.

 

[Dionysus]

To me it's not a matter of keeping the load under 100, what if a short happens. It will pass thru the 200 and may not trip the 100 timely.

I wasn't really even going to go into all what is wrong with and and can possibly go wrong. ESPECIALLY as it is a 3-phase system, and there is no mention to WHERE the two 100A 3-phase switches are fed from, and that they are physically separated.

Honestly time it takes for a 100A fuse to blow is my least concern.

 

[JD]

WHERE the two 100A 3-phase switches are fed from

This is where things can go REAL wrong- Worst case, two boxes fed from separate transformers. There is always a tolerance in the manufacture of transformers. (Less if same production lot.) Any variations and you will have eddy current flowing between them through your feeders. Even when off the same transformer, if one comes from a panel that has a heavy HVAC load, the voltage will be lower, and power will "redistribute" itself through the looped feeders. This can be a real problem if there is a flow along the neutral as there is no OCPD device to interrupt it. The second thing is the inherent danger during tear-down. "Switch is off, must be ok to disconnect and handle the cable." Once disconnected, if the other switch is on, you have live male connectors in your hands! (often called a "suicide cable.") Now cams have some protection on the males, but this is still dangerous. I am sure we could go on for hours, but since this event is now in the past (multi-day?) it is probably an exercise in history. Would defiantly avoid this in the future.

 

[cbrandt]

This is standard operating procedure at a major convention center that happens to have their biggest show of the year this week. The in house rules state that no single feed can be larger than 200 amps. To feed anything that needs 400, they provide us with 2x 200amp feeds that we have to tie together into one rack. Gives me the heeby jeebies every time, but they refuse to send 400 amps down 4/0.

 

[gafftapegreenia]

This is standard operating procedure at a major convention center that happens to have their biggest show of the year this week. The in house rules state that no single feed can be larger than 200 amps. To feed anything that needs 400, they provide us with 2x 200amp feeds that we have to tie together into one rack. Gives me the heeby jeebies every time, but they refuse to send 400 amps down 4/0.

Wow. Really? Wow.


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[STEVETERRY]

Wow. Really? Wow.


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I hope there are no ETCP electricians involved in this disaster!

To the OP: would you be willing to share the name of the facility?

ST

 

[jstroming]

The event ended today with no major issues.

SteveTerry I would prefer not to name them publicly as I do events there frequently but will PM you.

 

[Dionysus]

This is standard operating procedure at a major convention center that happens to have their biggest show of the year this week. The in house rules state that no single feed can be larger than 200 amps. To feed anything that needs 400, they provide us with 2x 200amp feeds that we have to tie together into one rack. Gives me the heeby jeebies every time, but they refuse to send 400 amps down 4/0.

All kinds of wrong. Its fine to parallel conductors FROM A SINGLE SOURCE, but not to take two smaller switches and attempt to put them together to "make a bigger service". Completely unacceptable.

Parallel conductors are actually very common in large service equipment, where the appropriate sized wire would be prohibitive either due to cost, size or being a PITA to work with. Ive pulled dual MCM250, 4/0, 3/0, etc. many times (not fun in a blizzard working with MCM250 I tell you).

 

[edinc90]

But this can't be right, can it?

I was working at a kid's dance convention. This box was stage right at the bottom of the stairs to get off stage. In order to give us 200 amp service, the house crew tee'd two 100 amp 3-phase lines together into this box. But they didn't have the right gender tee for the neutral, so they tee'd it twice, then turned it around, then left the unused male end exposed. We taped over it to avoid children putting their fingers into it. Maybe it's fine, no one died, and the lights worked, but it doesn't look like any feeder arrangement I've ever seen.

 

[StradivariusBone]

It would appear a friend of your's already was here...http://www.controlbooth.com/threads/urgent-electrical-question.36991/

I'm no electrician either, but having an understanding and healthy respect for what electricity can do would cause me to stay away from that mess.

Edit- It seems a mod moved this thread together, in case you were wondering why my initial comment made no sense.

 

[gafftapegreenia]

I still ponder as to what is feeding these two 100 amp boxes. But its bad no matter what.


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[JD]

I still ponder as to what is feeding these two 100 amp boxes. Certainly still bad practice, but could be varying degrees of bad based of the feed.

Seen split disconnects before (I'm sure you have too) where there is one on stage left and one on stage right. The concept is that you use the one that is the most convenient. In those venues that I have done, they are usually fed from the same panels but off different OCPDs. I have (now retired) never see a case where they were combined. I used to travel with several smaller racks so we could run them off various sources if the need arose. The though of teeing two feeds together off separate OCPDs would turn my stomach! Even if the sources were known (which they were not), you still have a laundry list of bad things that could happen. As far as the questions about T's goes, I am not sure there is anything specific about the configuration. The catch-all is that cams are considered a "tool-less lug" and therefore have the same requirements of authorized personnel as if you were bugging/lugging bare ends. One would hope that the "house electrician" would have sufficient certification and knowledge to keep things safe. As this thread brings to light, that is not always the case.

 

[gafftapegreenia]

I had to reread the thread a few times to understand what they did. Ok so it's one 200 amp box fed from two separate 100 amp panels. For some reason i wasn't clear on that. Yeah no matter how it's fed I don't like it. Yikes.



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[Senorfish]

Just give us a hint, is his name Dr. Frankenstein or Igor?

Honestly seeing that rig, I wouldn't touch anything metal in that venue at all. This is a situation that calls for bringing in a 3rd opinion- a professional electrician with the aim of giving the venue management some advice which in a nutshell would be, "you need to hire a real electrician".

 

[Dionysus]

But this can't be right, can it?

I was working at a kid's dance convention. This box was stage right at the bottom of the stairs to get off stage. In order to give us 200 amp service, the house crew tee'd two 100 amp 3-phase lines together into this box. But they didn't have the right gender tee for the neutral, so they tee'd it twice, then turned it around, then left the unused male end exposed. We taped over it to avoid children putting their fingers into it. Maybe it's fine, no one died, and the lights worked, but it doesn't look like any feeder arrangement I've ever seen.

In no way is that right, see my previous post.

WHY - in a nutshell in the most simple and definitive way I will explain why with a simple question.
"What could happen if a single 100a fuse were to blow in one of the two feeding disconnects?"