Single Pole VS Double Pole Circuit Breaker

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fifty60

Senior Member
Location
USA
If I have a single phase 460V (460V line to line) load, is there any reason to use a double pole circuit breaker over a single pole breaker?
 

Smart $

Esteemed Member
Location
Ohio
If I have a single phase 460V (460V line to line) load, is there any reason to use a double pole circuit breaker over a single pole breaker?
Common trip required on ungrounded systems {interpretation}. See 240.15(B), and (2) thereunder.
 

iwire

Moderator
Staff member
Location
Massachusetts
240.15 Ungrounded Conductors.

(B) Circuit Breaker as Overcurrent Device.
Circuit breakers
shall open all ungrounded conductors of the circuit both
manually and automatically unless otherwise permitted in
240.15(B)(1), (B)(2), (B)(3), and (B)(4).

I do not see anything in (1), (2), (3) or (4) that would change things for you.
 

iwire

Moderator
Staff member
Location
Massachusetts
As opposed to singular form, system?

I think either can be used in the vernacular of my reply... but if I drop the s, then I have to insert an an before ungrounded.

Than I am curious why you assume an ungrounded system. I thought you meant to type ungrounded conductors.

A solidly bonded Wye system often supplies single phase 480 line to line loads. The OP mentioned loads while you are mentioning systems.

Seems we need more info.
 

Smart $

Esteemed Member
Location
Ohio
Than I am curious why you assume an ungrounded system. I thought you meant to type ungrounded conductors.

A solidly bonded Wye system often supplies single phase 480 line to line loads. The OP mentioned loads while you are mentioning systems.

Seems we need more info.
Note the requirement for automatically in 240.15(B) general statement. Item (2) thereunder provides exception for grounded systems, which means breakers can be independent trip. Ergo, no exception for ungrounded systems. OP did not mention whether load is going to be connected to grounded or ungrounded system.
 

iwire

Moderator
Staff member
Location
Massachusetts
Note the requirement for automatically in 240.15(B) general statement. Item (2) thereunder provides exception for grounded systems. Ergo, no exception for ungrounded systems.

And still I am not understanding why you are assuming it is an ungrounded system.

It may well be an ungrounded system I just don't see anything from the OP pointing that way.

I will wait for the OP to chime in. :)
 

Smart $

Esteemed Member
Location
Ohio
And still I am not understanding why you are assuming it is an ungrounded system.

It may well be an ungrounded system I just don't see anything from the OP pointing that way.

I will wait for the OP to chime in. :)
Added last sentence to my post as you replied...
 

fifty60

Senior Member
Location
USA
It is a 460Y VAC system.."circuit breaker must open all ungrounded conductors" is pretty clear, I will use double poles for these loads

Is there anything similar for relays and contactors? Can I control a single phase motor, that is powered from 230V transformer, ungrounded (though the 115V center tap is ground) with a single pole from a relay, or would I need to open/close both ungrounded conductors?
 

iwire

Moderator
Staff member
Location
Massachusetts
In general 'controllers' are not required to open all conductors.

Disconnecting means are required to open all ungrounded and sometimes even the grounded conductor. (fuel dispensers)
 

Smart $

Esteemed Member
Location
Ohio
It is a 460Y VAC system.."circuit breaker must open all ungrounded conductors" is pretty clear, I will use double poles for these loads
To be clear, you are connecting to a [grounded] 480Y/277V 3? 4W system, right? A 460V system is non-standard, but it is a common rating on NEMA equipment for a load to be connected to a 480V source. Some non-NEMA equipment manufacturers mimic that NEMA rating.

Double pole breakers can be either independent or common trip.

Is there anything similar for relays and contactors? Can I control a single phase motor, that is powered from 230V transformer, ungrounded (though the 115V center tap is ground) with a single pole from a relay, or would I need to open/close both ungrounded conductors?
You can break only one pole, but common industry practice is to break both concurrently.
 

kwired

Electron manager
Location
NE Nebraska
It is a 460Y VAC system.."circuit breaker must open all ungrounded conductors" is pretty clear, I will use double poles for these loads

Is there anything similar for relays and contactors? Can I control a single phase motor, that is powered from 230V transformer, ungrounded (though the 115V center tap is ground) with a single pole from a relay, or would I need to open/close both ungrounded conductors?

Instructions on contactors sometimes may say something like "above 240 volts, break all lines". If that is part of listing instructions then I think 110.3(B) is the code to cite for violation if that instruction is not followed. A disconnecting means still needs to open all ungrounded conductors.
 

fifty60

Senior Member
Location
USA
Yes, 480Y/277, but there is a single pole fan that is powered from a 480 primary to 240Y/120 secondary transformer.

110.3 would be a catch all for situations like this... The load in question is a 1/8HP fan motor powered from the 240V transformer...I actually do not want to use a contactor on such a small load, and would prefer to use a 1HP rated relay. The relay I want to use is only a single pole relay, but if I needed to break both ungrounded conductors with my control then I would use a double pole relay instead.

It makes sense that the OCPD would need to be a 2 pole...
 

Smart $

Esteemed Member
Location
Ohio
Do you want to get into the design of the fan circuit?

Is the fan (via transformer) the only load on the 480V breaker? Only load on transformer? 240V or 120V?
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
It is a 460Y VAC system.."circuit breaker must open all ungrounded conductors" is pretty clear, I will use double poles for these loads

Is there anything similar for relays and contactors? Can I control a single phase motor, that is powered from 230V transformer, ungrounded (though the 115V center tap is ground) with a single pole from a relay, or would I need to open/close both ungrounded conductors?
You can do whatever makes the motor stop and start. The breaker (or fuse) is about protection. The contactor has nothing to do with PROTECTION of the circuit, only control of it.

An overload relay on a motor circuit is similar, but not exactly the same. So for example if you use an external OL relay on a single phase motor fed with 2 ungrounded conductors (i.e. L1, L2), you must have an OL sensing elements in EACH ungrounded conductor. But a basic OL relay is just a current sensing relay with a control contact, it provides over LOAD protection, but not short circuit or ground fault protection. So although it does not itself open the circuit, it is required to SENSE the condition of both wires, but is then used to drop out a contactor, which does stop the current flow. So because the contactor is just a control device, you can get cheap and use the OL to drop out a single pole contactor or relay if you want to. That is done all the time on low cost OEM equipment. I don't happen to like that approach, but I see it a lot and technically, there is nothing prohibiting it.

But it comes under that "Just because you can, doesn't mean you should" heading. (From Jim Dungar's sig line)
 

briank

New User
Location
Brookfield, WI
It is a 460Y VAC system.."circuit breaker must open all ungrounded conductors" is pretty clear, I will use double poles for these loads

Is there anything similar for relays and contactors? Can I control a single phase motor, that is powered from 230V transformer, ungrounded (though the 115V center tap is ground) with a single pole from a relay, or would I need to open/close both ungrounded conductors?

Only if you want to kill somebody. :eek:
 

kwired

Electron manager
Location
NE Nebraska
An overload relay on a motor circuit is similar, but not exactly the same. So for example if you use an external OL relay on a single phase motor fed with 2 ungrounded conductors (i.e. L1, L2), you must have an OL sensing elements in EACH ungrounded conductor.

You sure about that one? I know you must have sensing device in all three ungrounded conductors of a three phase motor(but at one time two was acceptable), but have seen many installs with only one overload sensing device in any portion of the circuit - current is the same everywhere in the circuit when supplying a two wire load unless there is a ground fault somewhere other then the two ends of the circuit. I believe 430.37 agrees with me. Short circuit and ground fault protection must be installed in each ungrounded conductor though, and can be the same device that provides overload protection though many times each type of protection is provided by separate devices.
 

Haji

Banned
Location
India
Smart $:
If there is already a GFCI upstream, single pole breaker instead of two pole breaker for an ungrounded 460V two wire system may be used. It results not only in safer operation but also may lower cost (single pole instead two pole breaker).
What do you think from the point of view of CMP?
:)
 
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