240 V Breaker Question

[teejer]

We are working on an enclosure for a customer and they are requesting a 240V circuit breaker (not 120/240V). They are claiming that they are going to feed this 240V circuit breaker with 3 phase 480 V. Now I understand that 1 phase to neutral in a 3 phase 480V system is typically 277V. Essentially, they are claiming that each phase to neutral would be 240V and not the standard 277V. Is this in fact possible? My math tells me that the phase to phase voltage would in fact be 415V if each phase to neutral is 240V, so perhaps they have their source voltage or math incorrect? They tell us that the breakers will protect lighting circuits that will only ever be wired for 240V and never 3 phase. If in fact each phase to neutral is 240V, then a circuit breaker rated 240V (not 120/240V) is adequate, correct?

 

[iwire]

They are claiming that they are going to feed this 240V circuit breaker with 3 phase 480 V.

I would not connect it up.

 

[jim dungar]

As Bob said - do not use a 240V breaker on a 480Y/277 system

In Europe a common lighting circuit would be fed from a 415Y/240V system. Several American manufacturers do offer "special" breakers and panels (which look like their standard products) for these systems.

You need to be sure of what system your customer has.

 

[Jraef]

On 480V delta (3 wire) systems, sometimes you will measure 240V phase to ground because it is essentially floating, but that is NOT a valid system voltage. So you should not and cannot use it as such. The voltage could also go to line voltagfe, so yopur 240V breakers would not likely isolate. Flash overs are a bad thing...

 

[hardworkingstiff]

Is this job in the USA?

 

[LarryFine]

If it were me, I'd spec a 600v breaker for this application. That phase-to-phase voltage is nothing to play around with.