3-Phase Disconnect fed from 3 different circuits

scnkapc

scnkapc

Member
Location
Northern Kentucky
We have a customer that is feeding a 3-phase disconnect from three different circuits in the same panel and the breakers are not grouped together - Not a 3-pole breaker. They are fed from circuit numbers 10, 20, 30. All are 20 amp circuits feeding a 30-amp disconnect with 15 amp fuse, which then feeds three roof top fans. This is a commercial building.

My question is: Where in the code does this say it is a violation for this type of installation?

Thanks and God Bless
 
tom baker

tom baker

First Chief Moderator
Staff member
Location
Bremerton, Washington
Not different from a three gang switch box, three single pole, toggle switches, each fed from a different circuit. A qualified electrician would know how to test for voltage.
 
C

Choice_Gorilla

Member
Location
New England
Occupation
Journeyman Electrician
Are the fans all 3 phase? Or do circuits 10, 20, and 30 each feed their own individual fan but use the one 3 phase disconnect as some sort of common disconnect for all fans?
 
kwired

kwired

Electron manager
Location
NE Nebraska
tom baker said:
Not different from a three gang switch box, three single pole, toggle switches, each fed from a different circuit. A qualified electrician would know how to test for voltage.
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3 separate switches in a 3 gang box isn't the same animal as a three pole switch either though.

More details possibly needed on OP's "disconnect" to answer his question?

Is it a three pole switch, safety switch, common trip breaker, three independent single pole switches or circuit breakers?

Handle ties possibly needed at very least on the supply circuit(s) and are much easier to find for adjacent breakers than ones to fit 10 spaces apart in the panelboard.
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
If they are 3 separate single pole loads, then don't think of it as a "3 phase" disconnect, think of it as a 3 POLE disconnect, as in 3 separate circuits. The 3 circuits might all be sourced from the same phase, or not, but so long as they are not feeding the SAME SINGLE LOAD, then it's fine. I've done this with a 6 pole disconnect before, killing power to 3 separate single phase (2 pole) loads. The thing is, you would have to clearly LABEL the remote disconnect as having 3 separate power sources, and (although I don't thing it's required, but for safety sake) label which they were in the origin panel.

If the 3 breakers are being combined at the disconnect to serve ONE 3 phase load, then it's a violation. Circuit breakers must simultaneously disconnect ALL ungrounded conductors in a circuit when they trip and it must be done at the ORIGIN of the circuit.
 
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kwired

kwired

Electron manager
Location
NE Nebraska
Jraef said:
If they are 3 separate single pole loads, then don't think of it as a "3 phase" disconnect, think of it as a 3 POLE disconnect, as in 3 separate circuits. The 3 circuits might all be sourced from the same phase, or not, but so long as they are not feeding the SAME SINGLE LOAD, then it's fine. I've done this with a 6 pole disconnect before, killing power to 3 separate single phase (2 pole) loads. The thing is, you would have to clearly LABEL the remote disconnect as having 3 separate power sources, and (although I don't thing it's required, but for safety sake) label which they were in the origin panel.

If the 3 breakers are being combined at the disconnect to serve ONE 3 phase load, then it's a violation. Circuit breakers must simultaneously disconnect ALL ungrounded conductors in a circuit when they trip and it must be done at the ORIGIN of the circuit.
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Does those 3 pole motor rated switches that fit in a device box fall under the same rules as other "snap switches"?

I asked for more details on exactly what the OP's "disconnect" was, but is possible it needs handle ties on the supply lines at the very least depending on more details.
 
J

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
If actually one circuit feeding three-phase loads, then handle ties are required if voltage to ground is not above 120V. Common trip required if voltage to ground is higher. See 240.15(B)(3).
 
Jpflex

Jpflex

Electrician big leagues
Location
Victorville
Occupation
Electrician commercial and residential
scnkapc said:
We have a customer that is feeding a 3-phase disconnect from three different circuits in the same panel and the breakers are not grouped together - Not a 3-pole breaker. They are fed from circuit numbers 10, 20, 30. All are 20 amp circuits feeding a 30-amp disconnect with 15 amp fuse, which then feeds three roof top fans. This is a commercial building.

My question is: Where in the code does this say it is a violation for this type of installation?

Thanks and God Bless
Click to expand...
Code would require a switch to simultaneously disconnect all ungrounded conductors. So If any of the circuits/ loads were not 120 volts but a 2 pole 240 circuit then it’s possible there could be a violation if one ungrounded conductor isn’t switched but I don’t think that’s what you have here
 
scnkapc

scnkapc

Member
Location
Northern Kentucky
Choice_Gorilla said:
Are the fans all 3 phase? Or do circuits 10, 20, and 30 each feed their own individual fan but use the one 3 phase disconnect as some sort of common disconnect for all fans?
Click to expand...
NO. The fans are not 3-phase. Each circuit feeds an individual fan motor on the roof. The neutrals merely run through the disconnected and are not spliced together because they are different phases.
 
J

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Yeah, I don't this as a code violation. A bit odd, perhaps, to have an apparently optional disconnect that gangs together three circuits. But not unsafe.
 
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