EGC sizing

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hhsting

Senior Member
I have 1200A static trip breaker with long time pickup set of 0.5x1200A = 600A. Question should the equipment grounding conductor be sized at 600A or 1200A? What if someone later changes from 0.5 to 1 then would equipment grounding conductor cable size need to be change ?
 

roger

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Look in the index for "what if" you will find your answer there

Roger
 

roger

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Staff member
Location
Fl
Occupation
Electrician
Ok but at present the circuit breaker set at 600A. I just wanted to make sure no code is violated if equipment grounding conductor is sized per 600A.
You can not worry about "what ifs". If you need an 80 amp fused safety switch for a feeder to a piece of equipment you will have to use a 100 amp rated switch and install 80 amp fuses, you can not control what happens down the road.

Roger
 

Carultch

Senior Member
Location
Massachusetts
It has to be restricted access to only qualified personnel, in order to take credit for the setting you select. Once it qualifies, all calculations that depend on the adjusted setting, are permitted to take credit for it. Ungrounded sizing, neutral sizing, EGC sizing, selective coordination of time-current curves, etc. Otherwise the highest possible rating applies.

240.6(C) spells out ways you could do this that qualify. IMO, qualifying with part C without even thinking about it, is the most common situation where you'll use an adjustable trip setting in the first place, because it would likely either be behind a locked electrical room door, or behind a lockable equipment door, or both. Any breaker in a panelboard intended for the general occupants of the building to use (like the ~200A panels in a dwelling unit), will likely be a fixed trip breaker.

The intent is the concern that the general public might change the setting unaware of the consequences, it would make the circuit unsafe, if not sized to worst-case-scenario.
 
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