Control/Dimming Overloading breaker pack

[STEVETERRY]

Not for nuttin, but at some point the parts and labor swapping to rated breakers may not be worth your while and the Lex Product box becomes cost effective. They are, if nothing else, very, very durable and worth the expense.

I stopped making my own orchestra music stand light distro's for this reason, finding the Lex E-Strings to be a better built solution for the long run. I see a LOT of these Lex boxes and I know they are heavily used in the film business, where stuff gets kicked around (unlike us civilized theatre folks)

@ Derek. I cannot understand the WiKi. I'm dense sometimes. I KNOW there's a rational reason as to why trying to pull 17 plus amps thru cable rated for 15 will heat the cable, making the breakers pop. I've experienced this. Please put on your "Academcian" cap for a second and learn us (or me).

Thanks in advance

Just to be clear, a piece of 14/3 type SO with two current-carrying conductors is rated at 18 amps per NEC table 400.5(A)(1) column B.

If a cable is used at more than its rated current it will overheat. This overheating can be transferred to circuit breaker thermal trip mechanism via the breaker terminals. This will cause the breaker to trip at lower than its rating. However, 17A on 14/3 is unlikely to cause this problem.


ST

 

[STEVETERRY]

Can you provide a source for this information. I am unable to find documentation from Schneider Electric (Square D) that confirms this, the available trip curve shows a continuous loading of between 1 and 1.25 times the rated current at an ambient temp of 104 degrees. I believe some of the confusion may be originating from the NEC design requirement that an OCPD not be loaded to more than 80% of its capacity if it will be subject to that load for more than three hours unless it is listed for continuous duty.

Dover

Thermal magnetic breakers are calibrated for a specific ambient temperature, usually 40 degrees C (104F). There is no way these devices will reliably hold more than 80% of rating at continuous duty.

ST

 

[STEVETERRY]

Ahhh see I was under the impression that it was a MWBC (shared neutral from the main's) If that is true then circuits that share a neutral must be tied together. Am I correct in that?

That is correct.

ST

 

[STEVETERRY]

Not required. The individual breakers may be single pole. Think of a regular building circuit panel fed by a 3 pole service. The main feed breaker is a 3 pole, but the individual branch circuits are not. The Lex distro shows this in a portable application.

Granted that it may be good advice as it will take out the entire pack, which may be a good thing depending upon the reasons for the trip.

A handle tie is required. if not, it would be possible to have an apparently dead pack still energized on one leg.

ST

 

[derekleffew]

A handle tie is required. if not, it would be possible to have an apparently dead pack still energized on one leg.

I'm more confused than ever. I believe this, or similar, is the dimmer pack in question:

Leprecon ULD 360.

I'm (almost) certain Mr. Terry does not mean to imply that the circuit breakers feeding the two receptacles that power the two lines feeding this pack must have a common trip. Often packs of this type are used in rooms where power is run to two different walls/circuits, and there's no guarantee the breakers will be adjacent to each other, or even in the same branch circuit panel.


Theoretically, consider powering the above pack via the lowly and common doghouse. If input is an L21-20 and output is three 5-20 duplex receptacles, no OCPD is required at all, as there's no reduction in rating. If, as shown below, input is L21-30 and output is three 5-20 duplex receptacles, three separate 20A fuses are required. (Disregarding the device's parallel L21-30 pass-thru outlet).

From Enclosure Manufacturer & Wholesale Supplier From Usa :

Doghouse (Fused), UL Listed (UL 1640) for exposition halls and similar locations. Enclosure is high impact, non-conductive, non-corrosive. The enclosure houses 3 each 20-ampere, 5-20 duplex receptacles (1 each - black, red and blue). Incoming to be 1 each 30-ampere L21-30 inlet. Output to be 1 each 30-ampere, L21-30 receptacle. The three 20-ampere duplexes are protected by three 20-ampere fuses and has three neon phase indicator lights.

Again, handle ties/common trip is required for the OCPD feeding the L21 input of the doghouse, but the common trip requirement ends there.

Mr. Terry, care to expound on the differences between UL508 and UL1640?

 

[STEVETERRY]

Mr. Terry, care to expound on the differences between UL508 and UL1640?

UL1640 covers portable power distribution units that contain wiring devices and overcurrent protective devices.

UL508 covers industrial control equipment, which in this case includes small dimmer packs.

ST

 

[JD]

You're both right. I think the wording referring to a common neutral is what sent things askew.

The pack Derek pictured is really two packs in the same case that share common control circuits. What is not shared is the neutral. All the dimmers on plug #1 return through the neutral on plug #1. Same is true on the other half.

If this pack were equipped with a 12/4 (HHNG) cable and/or a 4 blade twist, then a tied breaker would have to feed the hots.