#### Foxinabox10

##### Active Member
That's true...you could just replace the ones plugging into the system directly and leave the rest for now anywats.

#### ManOfLights

##### Member
Go and get replacement edison plugs and then get replacement twist lock plugs and an extention chord. cut the extention chord into 1.5 foot long peices. then wire on one end the edison replacement plug and on the other the twist lock.... there you go your custom adaptor... make sure before using it you test the curtitry so there are no shorts.

#### ship

##### Senior Team Emeritus
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.

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.