ST adapters


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My old school's theatre is donating their 12 old 4-circuit 12-lamp Strand/Century R40 borderlights to my high school, and they have twistlocks on them. Our electrics are all U-ground (Edison) connectors. The borderlights are set up to "daisy chain," basically meaning that one end has male plugs to plug into the electric or another instrument, and the other end has female plugs so more borderlights can be chained together (up to 2400w per circuit). Anyway, I want to use adapters since we'll be chaining four together on each electric, and we really don't have the money right now to buy 96 plugs at about $5 each. I would get 12 adapters that would go from U-ground male to twistlock female for each of the four circuits on the three electrics. In a theatrical supply catalog, I found adapters that were made from ST cable, and was wondering if that is legal for stage use. They look to be about a foot long from the picture they have in there. I know the three foot rule for any SJxxx cable, but I don't have a copy of the NEC (and I really wouldn't want to go digging even if I had it, that would give me a headache!), and I don't know if that applies for ST cable or not. They also have adapters made of SO cable, but they're considerably more expensive.

Here's the catalog:

They're on PDF page 39 (catalog page 36) near the bottom right corner. The PDF takes forever since it's pretty big, but be patient and it will eventually show up.
I know that adapters can be used, but the real question is, is ST cable legal on adapters?
describe to me your def of "st" cable.. are you talking romex?... when i think of ST cable that is a fiber patch cable.... and if you are concerned about it you could always buy the connectors and put whatever cable you feel like on it... or you can get solid adapters from bmi
ship said:
ST- Same as S cord, except with outer jacket of (thermoplastic) Materials. 18-2 Awg. 2 or more Conductors. Rated for Stage and Garage Use.

ST cable has a thermoplastic jacket, while SO has a neoprene/rubber jacket. Maybe ship can elaborate, if he's not too busy...

I guess that answers my question, just needed to do a bit of browsing and searching ;)

It seems to me you'd be much better off simply buying 12 male Edison (U ground) connectors and replacing the twist locks. I'm sure the cost of the adapters is $ 25.00 or more each where as you posted, an Edison connector is about 5 bucks.
That's could just replace the ones plugging into the system directly and leave the rest for now anywats.
ST cable:
ST- Same as S cord, except with outer jacket of (thermoplastic) Materials. 18-2 Awg. 2 or more Conductors. Rated for Stage and Garage Use.

If you can find any 12/3 ST on the market, than it’s rated for stage usage. Otherwise if less in wire size than at least 12 AWG, than it’s a really bad idea to use for a jumper between fixtures or adaptor on this type of fixture. If above a 18ga wire, it’s a really bad idea to use.

You have three classifications of the cable/plug going on here.

First is the 3' rule which is more or less a waver for short cords that due to their length would be good and can be type S extra hard duty, but are assumed at that length to be used in a responsible or at least protected from abuse way to allow for a lesser grade of cable. Less than a worry here. In general any 3' or less in length adaptor or jumper can be 3' or less including should you wish heat wire. This ST cable does not apply as a concern here given it’s already a extra hard service cord. This specification of ST instead of SJT dictates that it is other than “Junior Hard Service” and other than in a minimum AWG 16 GA requirement for all “Extra Hard Service” such as type “S” or in this case (if possible) type ST jumpers on stage, it’s 100% compliant by way of length in SJ (Hard Service) or type S (Extra Hard Service) Jumpers over 3' in length.

Next is wire size. While it’s not known for sure what type of plug you are using the old fixtures had in adapting them to Edison, given a mentioned 2.4Kw dimmer size, you must have a 2.4Kw rated plug on both ends of the adaptor to be fully code compliant. This in addition to the adaptor cable that’s using at least a #12 AWG wire rated also for that type of loading. If my note above is true and the only case of a true ST cable in size, than a 18ga wire is only rated for somewhere between 300 and 700w in load. This would far fall below that of a 2.4Kw dimmer capacity and thus be unsafe. Not the thermoplastic wire jacket but instead the gauge of the wire used. Should this ST be rated for at leat #12 AWG in wire, than all is fine here at least.

Also a normal Edison plug/outlet is in parallel blade U-Ground is only rated for 15 Amps or 1.8Kw. In other words, if fully loaded to dimmer capacity, they would not work out very well for a 2.4Kw dimmer. This said, and only by way of institution waver you work for, a industrial grade 15 Amp plug is the exact same plug as a 20Amp plug - just different pin configuration. This only if commercial/industrial grade were at times it is the same plug. If it’s only a question of parallel blade as opposed to T-Shape 20-Amp blade configuration, the 15A commercial plug will handle 20 amps just fine. Again given the place you work/go to school at has approved of this plug for 20 amp usage as opposed to a code requirement for plugs rated for the amperage. Otherwise, as Edison, you will be needing the male and female commercial version of the 20Amp T-Shaped as opposed to Parallel U-Ground version. Most outlets on a 2.4Kw Edison system will already be having 20Amp outlets on them thus 20A plugs will plug into them anyway. Do your stage dimmer receptacles in wired to 2.4Kw dimmers have a T-Shape to the neutral prong or just a parallel polorized outlet? The T-Shape Edison outlet is a 15 and 20 amp plug capable outlet. (Been about 30 year in the industry stage hands that had never seen a 20 amp Edison plug and thus wasted a bunch of time in re-wiring provided 20 Amp plugs to 15Amp in fitting into 20 Amp outlets.) Been there, done that, thus the above about company wavers for what plug is used. I no longer waste our time in providing the proper plugs for a outlet even if code.

General concept, if 2.4Kw dimmer, and plugging in a 2.4Kw load, you really should be using a 20 Amp NEMA 5-20 plug if Edision base in system, and must be using at least 12AWG cable. I don’t think I have ever seen a 12/3 ST cable, but that’s beyond the point. At least at this point, if it exists, it’s safe for a 20 amp load.

Now jacket. I’m fairly certain given the above that you actually saw a listing for SJT wire in the adaptors given the wire gauge. If not avoid it.

Wire can be grade S as in in rubberized or SE rubberized thermoset or ST in thermoplastic. All have the same base in amperage and even operating temperature. For code, it does not care about the material used only the thickness of it used for lengths over 3'. SJ cable in any of the types SJ, SJE, SJT are a sub class that is classified as “hard service” instead of otherwise “extra hard service” cord required. All for the most part also have the same operating temperatures of usage.

In other words if 90c wire, it’s only rated for that in safely insulating the conductors no matter the material making up it’s jacket. Rubber after this loses it’s dielectric insulating properties such as if it gets wet, it will allow say water to penetrate and conduct, or the other two plastic types will just plain melt in exposing the conductor.

The reason SJT and even SJE cable never caught on in the industry is that melting point as opposed to while not rated for more of a temperature, the rubber based cables will not be melting thus retain it’s shape and perhaps more of it’s insulation.

Figure a round cable exposed to a Leko cap for temperature. The plastic ones melt and exposes the conductors to the lamp cap for a short. The rubber one does not melt, has less surface area given a round cord exposed to the heat source thus can even if rated for the same temperature, withstand more heat or direct contact to it. A round surface that won’t melt has less surface area in contact with the heat source thus the heat is dissipated about the insulator. Yes, some part of this cable is overheated and in fact that zone of area is dielectrically broken down to some extent, but still the insulation has not gotten hot enough to melt and expose conductor inside it to fixture.

SJT cable normally you will find on your computer monitor or a light duty moving light to power it up. SJE cable you will find on most if they are not SJT cable, now SJE orange extension cords. SJE you will often find has SJT written after it in that it’s slightly different but still compliant with being a plastic cable. SJE is always a SJT but SJT is not always SJE. Neither are really a SJ cable by way of melting given the plastic nature.

Given you can ensure this cable will not touch the heat of a fixture, the NEC has no wording in what material makes up the cable for stage usage if under 3' in length. Not the best in fixture whip or cable but is acceptable. By way of class, SJE cable is more supple and more like rubberized cable than that of SJT thus it coils better and is for all intensive purposes a sufficient jumper. Many pre-made cords will be SJT or SJE in being cheaper to make.

Better stuff is S or SJ cable of course but it also becomes a cost effectiveness factor. As long as you can ensure that a thermoset cable does not touch a heat source, you are just fine in saving money. Otherwise if a little less in supervision, what can be assured it won’t easily melt is safer.

As for this project, yep, changing the plugs as opposed to buying adaptors would be a much better solution. Again if 20A outlets it’s better to use 20A plug. Otherwise most commercial grade or industrial grade plugs as required for stage usage anyway (not what’s cheapest at Home Depot) in the 15A version will work fine. In being code compliant, it for this application has to be a commercial grade or industrial grade plug anyway so this should not be of concern.

For commercial grade plugs 15A parallel blade, U-Ground - I get them for under $5.00 as a volume dealer, but doubt most end users get them at this. Pay the extra money especially for this high amperage situation for a good plug. This in addition to being more code compliant with using the 20A version of the Edison plug a NEMA 5-20.

Where possible avoide less than commercial/industrial grade plugs and avoid the thermoplasic cables both of the as it were by way of question SE and ST types. Such cables just don’t get along with lighting equipment.

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