2 wires under 1 lug

[chicagosparky]

Have a telecommunications client that has numerous sites wanting us to add a relay in their cabinets for a power loss alarm notification means. Their existing cabinets have a 200A, single phase MCB which is fed with 3/0 CU conductors. They are asking us to put a #14 in parallel with each of the feeder conductors and run it over to a new 15 A CB & new relay we install inside the cabinet as shown below. They provided us with these diagrams.
Even though the #14 will only be ran approx. 18 inches inside the cabinet to a 15 amp CB, the tap rule would not apply here & still unable to put a 2nd wire under one lug. Is this a correct assumption?

 

[infinity]

As you've surmised the connection method of the #14 conductors is a problem. You'll need to find another way to connect the #14 conductors.

 

[chicagosparky]

Thanks Rob.

 

[jim dungar]

Most breaker manufacturers have methods for attaching 'control wires' to their devices. I have seen adapters that slide underneath the lug and provide a 1/4" quick connect tab. I have also seen ones that are attached to breaker lugs (usually >250A) by screws.

 

[tom baker]

Yes there are adapters for breakers to allow connecting control wires
The 14 AWG will not be large enough. This may be more or a UL 508A question, but 508 and NEC rules are often similar. Section 430 deals with motor control circuits and OCP, since the control wire won't be leaving the enclousure you can use table 430.72B column B, indicates 400 percent of value specified in Table 310.15(B)(17) for 60°C conductors.

 

[chicagosparky]

So, for clarification purposes, as long as we get the breaker adapters as mentioned & per Note 2 of Table 430.72B, we could use a #8 [400% x 60A=240A], then we would be all good.

Thank you for the clarifications.

 

[Jraef]

To be clear though, you must use something that is APPROVED / LISTED with that circuit breaker for this purpose. I have run into many AHJs who are STICKLERS about that issue. The main point is that the standard lugs on a circuit breaker are NOT approved for multiple conductors in the same hole, and the few that are will require that they are both the SAME size. So when enforcement of this issue began in earnest about 20 years ago (from my experience) SOME of the breaker manufacturers came up with accessories or different versions of their lugs that had "power tap off" points for this purpose. In many cases it will involve replacing the breaker lugs.

I can't make out the breaker brand in your photo but here is a picture of the ones available from ABB for their breakers, many of them are similar, having a smaller screw in the lug that is meant for tapping off to feed a CPT primary or something. I used to just drill and tap my own, or just stuff the smaller wire in with the bigger one, that's what they clamped down on. It must be listed with the breaker now.

 

[petersonra]

there are also UL listed vampire connectors you could potentially use to connect a smaller wire to the big wires. But, as you noted, the tap rules are a pain to deal with. might be easier if there is an unused space to just add a breaker and not have to worry about a tap.

 

[Chamuit]

there are also UL listed vampire connectors you could potentially use to connect a smaller wire to the big wires. But, as you noted, the tap rules are a pain to deal with. might be easier if there is an unused space to just add a breaker and not have to worry about a tap.

That was my first thought as well. Is there a rationale for putting it on the line side of the main? If you have a power loss, you would see it on the load side. If there was still power and the main tripped, you would see it on the load side.

 

[petersonra]

and putting it on the line side means you won't be able to detect if the main trips or is opened.

 

[steve66]

That was my first thought as well. Is there a rationale for putting it on the line side of the main? If you have a power loss, you would see it on the load side. If there was still power and the main tripped, you would see it on the load side.

It looks like there are 2 different sources, and 2 main breakers that have an interlock.

Maybe I'm missing something, but I would think 240.21B1 would allow the #14 wire if it terminates on a 15a breaker in the same enclosure? (Assuming its connected to the lug in a legal way.)

Edit: And if I'm wrong, and we are basing the wire size on the OCP size, is there another 200A breaker upstream of each supply protection the existing 3/0?

And I just had another thought - Does the NEC or UL508 even apply if its in a telecom switching facility?

 

[chicagosparky]

Thanks again for the additional info. Our client feels if it's paralleled to the incoming power they could then decipher between a utility loss or an internal CB trip.
I personally like the idea of putting it on a 20 A CB, just that some of the various locations don't have spares, these are large cabinets and are custom fabricated and provided to us by the client so it's not an easy swap out of the internal 12 cct to a 20 cct panel. Space is limited.

 

[chicagosparky]

In response to Steve, some of the cabinets have an internal manual transfer switch so that's why it appears there are two mains. They have the cabinets fabricated with a generator plug mounted to the exterior of the cabinet in some locations where they don't have on site generators. Depending on the location & susceptibility of loss of power, delegates if they place a gen set on site or not. if not, then the manual XFER switch is used & they have someone pull up with a trailer mtd. gen set, plug it into the plug & hit the manual switch.

 

[Andy Delle]

Just put a self drilling screw into the feeders and a spade lug under it

Seriously I had a similar situation once and we used #12 solid. The #12 was about the thickness of one of the strands in the feeder so we figured it was OK as like here the #12 went about a foot to an internal fuse block, but code wise????

 

[Andy Delle]

You often need to have an always live power source in a shunt trip system for signalling. I guess the proper way if not using an approved tap method is another small service rated panel to feed the control system.