i'm working on a arc flash report. in field survey it was found that several 120/208V panelboards fed by transformers do not have a main circuit breaker. Neutrals and grounds are bonded but only neutral goes back to transformer with conduit serving as equipment ground. grounding electrode was not observed at most of these transformers. a lot of these panelboards are 70's or early 80's vintage ITE CDP-4 but there are other brands installed. In the past was there ever a time when panelboard didn't need main breaker or upstream breaker, or are these just incorrect installations? did neutral-ground bonding requirements change (e.g. i'm thinking of old stoves that had neutral-ground strap for 2W + G cord). thanks as always for the input.
Code history: neutral-ground bond
- Thread starter DW98
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- Location
- Lockport, IL
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- Semi-Retired Electrical Engineer
I don't have ready access to my older code books, and can't answer your specific question.
I am guessing that these panels have more than 6 breakers. So I will venture to say that if a panel is served directly from a transformer and does not have a main breaker, then the N-G bond question is probably not the biggest concern. This installation does not have overcurrent protection for the transformer secondary windings, the secondary conductors between the transformer and the panel, or the panel itself.
I am guessing that these panels have more than 6 breakers. So I will venture to say that if a panel is served directly from a transformer and does not have a main breaker, then the N-G bond question is probably not the biggest concern. This installation does not have overcurrent protection for the transformer secondary windings, the secondary conductors between the transformer and the panel, or the panel itself.
petersonra
Senior Member
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- Northern illinois
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- Semi-retired engineer
is it possible they are backfed?
- Location
- Wisconsin
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- PE (Retired) - Power Systems
I do not find it uncommon to find installations, from before the 70's, with no single main secondary on the output of transformers, particularly in industrial installations.
Neutral to ground bonding could be done at the transformer or at the switchboard/panel/disconnect.
Interesting question what is the age range of the installation(s)?
Any idea what year NEC would have been in effect?
Whats the primary voltage?
The requirements for overcurrent protection of panelboards can be found in 2017 NEC 408.36(B). The exception there that points to 240.21(C) is for single voltage transformers.
I have a 1978 NEC handy and it almost says the same thing under 384-16(d) Exception. However it seems to be more restrictive only allowing single phase single voltage.
Thanks for all the responses. This is an industrial setting. Alot of the panelboards in question appear to be mid 1970s era. Primary is 480V, secondaries are typically 120/240-1PH-3W or 120/208-3PH-4W.
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