The safety of outlet taps in entertainment lighting

[calkew5]

When I started my current job in June of last year, I was surprised to find out that a lot of our "two-fers" were actually edison outlet taps (the entire space is edison). I reluctantly accepted this fact for the present but resolved to solve it in the future. Over the course of the season, I used some of my dead time in between productions to fashion "real" V-style twofers from surplus plugs and cable. I'm now proud to say that the taps are entirely gone.

But I got to thinking, as I was spending all this time making two-fers, that I couldn't entirely blame my predecessors for thinking outlet taps were a good choice; after all...

1. They are UL-listed (I believe) and rated at 15 amps, which isn't a FULL dimmer load, but enough for three source fours or similar instruments, which is about the limit I'd put on a dimmer anyway. Besides, it's not wrong to use, say, 14-gauge cable with a 20 amp dimmer, because in a professional environment it's assumed you know what you're doing and won't overload it.

2. They are cheap, costing only about as much as a single edison plug (on a two-fer there are three plugs, two of which are the typically more expensive female, plus a few feet of cable, which also costs).

3. You don't have to spend any time to make them, and finally...

4. They are professionally manufactured and have no flexible parts. Why is it that we would consider a two-fer made by hand perfectly safe and preferable, and not a solid block of plastic with no wires to come loose? I can think of so many failure points of a self-made two-fer; after all, they aren't even made in such a way that uses the male plug in a manufacturer-intended way.

I've seen two-fers made in horrible ways, with no strain relief because someone tried to use 12-gauge SO and it wouldn't fit, so they just took off a few inches of rubber and replaced it with e-tape, then clamped the strain relief down on the inner conductors. What would you reccommend then, these jury-rigged devices or an outlet tap?



Trust me, I'm firmly of the belief that what goes in your grid should not be the same thing used to power your toaster oven, but I'm looking for solid justification for this belief. Thoughts?

 

[Footer]

I hope you did not throw away the power cubes.

Home made two-fers are actually illegal to use. I know everyone does it, but it is against the NEC to make multiple connections inside a connector except when a connector is designed for that use (socapex breakouts for example). This is the reason why professionally made twofers have the split in a molded lump in the middle of the cable.

Now, the other issue is the 15amp rating. Everything down stream of a breaker should be rated for the maximum rating of that circuit. So, you have a 20amp breaker, you can not connect 16 gauge cable because its to rated to handle 20 amps of power. You are right that you should not use triple taps with a lighting system. Instead, you should buy properly made molded two-fers.

All is not lost however, many places sell just the cable part, you provide your own ends. I have am buying another 15 of these at the end of this season to fix the rest of my stock.
2-fer, Molded, 36", Blunt Ends

18 bucks is cheap for piece of mind.

 

[MNicolai]

There's not much room for error should the voltage drop, as it often does in long cable runs and through dimmer packs. This is especially in a theatre where a user might unknowingly have 750w lamps floating around.

While I agree that there is some expectation that users are deemed competent, but most professional theatres know better and are easily able to use the right equipment, while schools and small community theatres are the ones that are often guilty of using these. In schools and small community theatres, I've seen these outlet taps -- two, three, four plugged into each other at a time. A school theatre filled with these taps could very quickly make a probably safe situation extremely dangerous.

Also, these taps are intended for a 15A environment on 5-15 connectors, where overloading the taps is synonymous with overloading the circuit breaker. In residences, this is not a problem when most circuits are 15A, but in schools and commercial buildings almost all circuits are 20A. Likewise, almost all theatrical circuits are 20A. That means you can overload these taps without knowing it. In that regard, there is a problem with 5-15 parallel blade connectors being able to plug into 5-20 receptacles.

 

[JD]

On the bright side, most of these do have a 15 amp push button breaker, limiting them to 15 amps.

Now for the downside-

Constant loads are a funny thing. (As in three S4's on for an hour.) What should work sometimes burns up anyway. Most of these strips are very cheap inside. Most using a marginal gauge thin metal strip to supply all of the outlets.

Although I wouldn't think twice about using one to plug my computer and printer in, I would never use one in the stage environment. (imho)

 

[derekleffew]

... Everything down stream of a breaker should be rated for the maximum rating of that circuit. ...

If that were true, 5-15 devices would NEVER be permitted on a circuit with a 20A OPD. Not to mention plugging in the SourceFour having 16g wire from the plug to the socket.

... There's not much room for error should the voltage drop, as it often does in long cable runs and through dimmer packs. ...

It doesn't work that way. As voltage decreases, so does the wattage:

watts/WATTS = (volts/VOLTS)^1.6
(not 'squared' as you would get with a fixed resistance)

For the record, I have nothing against using good quality cube taps in lieu of Edison twofers. Except for the fact that they're often too short, requiring jumpers. And some AHJs, especially in exhibit halls and convention centers, won't allow them. Their house, their rules.

 

[len]

We use cube taps all the time. But 99% of the time the load on them is an LED fixture, which draws 35 - 50 watts, so no big deal.

Chances are, if you're using conventional fixtures and edison cube taps, you're using shoebox dimmers (at least in my case it's true), which means most of the time it's one fixture per circuit anyway, so cube taps or two-fers would be useless.

The problem I run into with good cube taps is that they're good and they tend to disappear.

 

[Footer]

If that were true, 5-15 devices would NEVER be permitted on a circuit with a 20A OPD. Not to mention plugging in the SourceFour having 16g wire from the plug to the socket.

The 15amp connector debate is one we have gone around and around on. There is also a difference between a cable with a known load on the end and a cable that could have any load on the end.

 

[MNicolai]

Derek, you raise a good point. My logic is faulty in that it suggests if voltage drops, current will be inversely proportional to it, eventually approaching infinity. That assumes constant brightness (and power), which is not the case. If that was true, you'd never be able to dim lights because as the dimmers reduced voltage, current would increase. The actual power draw relates purely to voltage and the hot resistance of the filament.

My point remains pretty much the same, though. It's less than .625 amps for a margin of safety assuming ideal conditions. Also, if these cube taps are close to the lighting fixtures, they will have to stand up to not only being pushed to their rated current draw, which will produce heat in the device, but also have to additionally withstand the high ambient temperatures of nearby lighting fixtures.

JD, I don't know which cube taps you buy, but I don't think I've ever seen a cube tap with a push-to-reset breaker. Any that do have that feature will have additional problems in tripping at less than 15A. Unlike ETC dimmers, most circuit breakers are not rated for 100% loading -- if left at a slightly lower current draw for a long enough amount of time, it's likely they'll trip the 15A breakers, again, because there isn't enough leftover margin for error.

I'd prefer saving cube taps for low-current applications. While they certainly can be useful, I'd always want to have more room for error. Here is something that is sort of an odd twist, though:

Assuming ideal conditions:
(575w * 3 fixtures) / 120v = 14.375A
(750w * 2 fixtures) / 120v = 12.5A

You would actually be better off plugging two 750w loads into the taps instead of three 575w loads. This gives you enough overhead that you'll not be as likely to prematurely trip a 15A breaker.

 

[JD]

JD, I don't know which cube taps you buy, but I don't think I've ever seen a cube tap with a push-to-reset breaker. Any that do have that feature will have additional problems in tripping at less than 15A. Unlike ETC dimmers, most circuit breakers are not rated for 100% loading -- if left at a slightly lower current draw for a long enough amount of time, it's likely they'll trip the 15A breakers, again, because there isn't enough leftover margin for error.

The word "Cube" did not get added until later in the thread. My first take was the standard Edison strip, usually containing six outlets. Cubes, on the other hand, I have no problem with. (Usually with 250w movers and such)

Regarding Amps/volts and long runs, there is one exception which is an electronic ballast. These will increase current draw as the voltage drops by way of their switch mode supply operation. Also, many spots (like some super troupers) will have a tap switch that will alter the current draw dependent on the voltage. Still, when referring to non-discharge stage lights, current & brightness drop as the voltage goes down.

(Of course, anyone plugging a Super Trouper into a cube tap.... Well, enough said ! )

 

[dramatech]

Footer, I have two of those molded 2fers that you pictured, one of them took out the Solid State Relay in one of my dimmers. When I determined that it was shorted internally, I used a razor knife and cut open the out vulcanized rubber jacket. Inside I found a plastic housing in two parts, that clamshell around three of the metal connection sleeves with a set screw on each end. The wires from the two output cables were twisted together and pushed into the sleeve and the screw was tightened down on the wire, with neither a ferrule or tinning. End result was that the wires had pulled out of the sleeve and shorted. The two I have were given to me as a gift, so I don't know if they may have been a cheaper version of a better brand, or the good stuff that escaped quality control. I Repaired the whole thing with ferrules and tightened everything down, replaced the outercover with with silicone adhesive.
I am still a little "gunshy" about using the one that has not failed, with the anticipation that it may have been assembled in the same careless manner. No real conclusions drawn, just a mild warning.

 

[SteveB]

Home made two-fers are actually illegal to use. I know everyone does it, but it is against the NEC to make multiple connections inside a connector except when a connector is designed for that use (socapex breakouts for example). This is the reason why professionally made twofers have the split in a molded lump in the middle of the cable.
.

Perhaps Steve Terry could clarify/confirm this, as I thought that there was an allowance in the NEC for 2-fers 18" or less in length to use the male connector as the connecting point for 2 SJ 12/3 cables.

Reason I ask as I purchased a whole lot of new 2-fers all made by TMB with splice in the male and would be surprised if they were all illegal.

SB

 

[calkew5]

I remember reading in another thread that V-style twofers were explicitly allowed by the NEC. I don't think they're illegal. But then again I don't think cube taps and the like are explicitly disallowed either.

For the record I was talking about cube taps, but I didn't want to say cube taps because not all of them are cubes, per se; but I'm talking about a small plastic device with one male plug and three female receptacles.

 

[derekleffew]

Of these, the only one I approve of is the orange one, and someone makes them in black.

Coding Horror: Road Warrior Revisited

JD was, of course, talking about a power strip/MOS/Waber strip.

 

[SteveB]

Perhaps Steve Terry could clarify/confirm this, as I thought that there was an allowance in the NEC for 2-fers 18" or less in length to use the male connector as the connecting point for 2 SJ 12/3 cables.

Reason I ask as I purchased a whole lot of new 2-fers all made by TMB with splice in the male and would be surprised if they were all illegal.

SB

Steve had this to say in a prior CB post:

" Twofers are a recognized construction in the theatre, as evidenced by section 520.69, which allows reduced diameter Junior Hard Service cord for twofers specifically so that two cables can enter the male connector. In this case, article 520 modifies Chapters 1 through 4 of the code for the theatre, a Special Occupancy."

And as comment on the OP, one thing that bothered me was the assumption that just because all the outlets were Edison, that they were 15 amp, noting that there are 20 amp versions. If the system was installed professionally and to code, these should have been 20 amp duplex, if the dimmers have 20 amp breakers and all wiring was appropriately sized.

Thus care must be taken in the use of connectors, cabling and cube taps downstream of the load breaker, as 15 amp devices are generally not allowed by NEC, for use on stage lighting equipment, when used on a stage or space that meets the definitions of section 520.

Just a thought.

 

[shiben]

And as comment on the OP, one thing that bothered me was the assumption that just because all the outlets were Edison, that they were 15 amp, noting that there are 20 amp versions. If the system was installed professionally and to code, these should have been 20 amp duplex, if the dimmers have 20 amp breakers and all wiring was appropriately sized.

20A Edison style connectors dont have 2 parallel blades, however, one is perpendicular to the other.

As for the 2fer illegality debate, I really hope that they are, just about ever house in town has bought or made them in a v style.

 

[SteveB]

20A Edison style connectors dont have 2 parallel blades, however, one is perpendicular to the other.

.

Only on the males. The female receptacles have both configurations to allow use of 15 amp male plugs.

 

[mrb]

couple quick notes:
15 amp edisons have the same current carrying capacity as a 20 amp edison. The metal inside is the same, the keying exists to keep you from plugging something that requires a 20 amp circuit into a 15 amp circuit.

The issue with the V style twofers is the listing of the plug. I dont think youre going to find an edison plug listed for multiple cords in the strain relief, and two conductors in the terminals.

NEC allows 15 amp receptacles on a 20 amp circuit, unless it is a single receptacle (a duplex is ok).

 

[erosing]

The issue with the V style twofers is the listing of the plug. I dont think youre going to find an edison plug listed for multiple cords in the strain relief, and two conductors in the terminals.

If anyone knows of a company that makes one, I'd be very interested.

 

[cdub260]

If anyone knows of a company that makes one, I'd be very interested.

Off hand, I'd say there probably isn't one. That said, there is an alternative if you absolutely have to make your own twofers. Heatshrink breakout boots will allow you to safely cover your splices and since they are adhesive lined, they also act as a strain relief for you splice. As with all things electrical, only qualified individuals should be making their own twofers.

However, I personally would not choose to use these breakout boots for standard twofers. Why? They're expensive. Once you factor in the cost of the wire, you're probably only saving $2.00 or so per twofer. Factor in what your employer pays for your time in making the twofers and it's probably a wash or cheaper to just by the pre-made assemblies. I use breakout boots quite often as I have to make a lot of custom cable assemblies. And they work very well for my needs. As an example, for last year's Pageant of the Masters I needed a 30 ft. cable with breakout points every 10 ft. I could have done this with three ten ft. cables and two twofers, but I had to be able to set it up and break it down in less than a minute on a nightly basis for nearly two months straight. For this application, two breakout boots, 30 ft. of cable, and a few connectors were an ideal solution. I still have the cable should I ever need it again. For a more conventional cable run, one that would stay in place for the run of a show, I would never go to this much effort, as my time could be better spent on other projects.

 

[erosing]

Off hand, I'd say there probably isn't one. That said, there is an alternative if you absolutely have to make your own twofers.

It was more of a curiosity (I was trying to find some for a stubborn company a while ago), I prefer them to be molded, and I don't make or use homemade ones. Thanks for the link on the boots though, I knew they were out there but never put much into finding them. Certainly not really worth it for making a straight up twofer, I would ahve to agree with you.