Aren't these style of distribution blocks a violation of the NEC?

Aren't these style of distribution blocks a violation go the NEC?


https://www.automationdirect.com/ad...e,_ul_listed,_175a-760a_(epdb_series)/epdb306

Like I can't have an 80A breaker with 4AWG in to this and then have 12AWG feed to 20A breakers? Right?





Or can you reduce the wire gauge as long as it immediately goes to feeding a breaker?

theColonel26 said:

Aren't these style of distribution blocks a violation go the NEC?


https://www.automationdirect.com/ad...e,_ul_listed,_175a-760a_(epdb_series)/epdb306

Like I can't have an 80A breaker with 4AWG in to this and then have 12AWG feed to 20A breakers? Right?





Or can you reduce the wire gauge as long as it immediately goes to feeding a breaker?

Click to expand...

If what you are saying is correct, then every distribution block that allows smaller wires on the output side would be wrong. But this is not the case and would make absurd things necessary like a your 20A circuit breaker with a 4AWG terminal. or what if the feeder was 500MCM and you had a 5A branch circuit. You don't see 5A fuse blocks with terminals that can handle 500MCM.

It's a little bit of a compromise but you can use the proper size wiring for your branch circuit from the distribution block to your branch circuit protector. So yes, this wire will be smaller than required by the immediate upstream protection. About the only think that can happen is a short, but these types of shorts also pull a huge amount of current so they very likely to blow the upstream protection.

Kind a makes you appreciate proper PPE

theColonel26 said:

Aren't these style of distribution blocks a violation go the NEC?


https://www.automationdirect.com/ad...e,_ul_listed,_175a-760a_(epdb_series)/epdb306

Like I can't have an 80A breaker with 4AWG in to this and then have 12AWG feed to 20A breakers? Right?


Or can you reduce the wire gauge as long as it immediately goes to feeding a breaker?

Click to expand...

In the NEC there are allowances for the use of smaller wires off of distribution blocks. Search for 6 foot tap rule and maybe even 20 ft taps. Since I don’t have my code book handy I can’t give you the exact section number.

Do some research on UL508A and or NFPA 79 feeder and branch circuit protection. If your using these in an industrial control panel these are the standards that apply.

NFPA 79 will explain that the downstream overcurrent device will provide protection for the upstream wire and has tables for the wire sizing.

Use them all the time in things like splitters. There are rules for how long the smaller conductors can be, as well as sizing. I think the standards in Canadian Electrical Code is not too different from NEC. Typically they are feeding into disconnect switches or something that has an automatic disconnecting means (breaker, fuse, etc) which has it's own rules as to sizing of conductors as well. It's always a case of the most economical while maintaining safety.

Thanks guys :site:

These all make use of the NEC "Tap Rule". You can tap a smaller wire off a larger wire as long as it goes to the protection for that size wire first. How big of a tap wire you can use is related to distance. In most cases where these distribution blocks are used, the distance is not that far.
I will have to dig up the section for tap rules..

Here is NEC verbiage..
https://library.e.abb.com/public/9e7ae3c8094341488549ef5a3e791064/ABB-1742-WPO_NEC_Tap_Rules.pdf

Here is a long explanation, but very informative
https://www.youtube.com/watch?v=_HkeAs1xYUE