Wire Ampacity for Service Disconnect Conductors

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fifty60

fifty60

Senior Member
Location
USA
I am being told that if I supply a service disconnect with my equipment, that I have to size the conductors to the disconnect to the maximum size fuse that fits inside the disconnect.

For example, if my machine needs a 120A fuse, and I use a 200A disconnect, then the conductors to the disconnect need to be sized for a 200A ampacity.

I can see this as being a good practice, to an extent, but I don't think it is mandated anywhere in the NFPA 70. I have never seen this in NFPA 79, or UL 508A either....Since it is a service disconnect, NFPA 70 would be the ultimate authority...

Does anyone know if this is an actual rule in NFPA 70? If i specify a fuse size for the equipment, I still have to size my wire ampacity to the disconnect and not the fuses? Sounds like an invitation for someone to monkey around with the fuse size on the equipment...
 
tom baker

tom baker

First Chief Moderator
Staff member
Location
Bremerton, Washington
You size the wire for the calculated load and then round up to the next standard OCPD. I don't have my code book so I can't give you the sections, someone else will.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
Is this truly a service disconnect or a service-rated disconnect being used as a non-service disconnecting means?

OP says your equipment is supplying the service disconnect. There is a limited amount of equipment that can be installed on the line side of a service disconnecting means. Exactly what is your equipment called or categorized as in this regards?
 
fifty60

fifty60

Senior Member
Location
USA
It is the line of sight disconnect for refrigeration equipment that is classified as "Lab Equipment". We sometime install the disconnect directly on the machine's sub panel, with a handle sticking out of the panel door. These are the disconnects I am referring to...
 
Smart $

Smart $

Esteemed Member
Location
Ohio
fifty60 said:
It is the line of sight disconnect for refrigeration equipment that is classified as "Lab Equipment". We sometime install the disconnect directly on the machine's sub panel, with a handle sticking out of the panel door. These are the disconnects I am referring to...
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For future reference, this would definitely not be a service disconnect, which refers to the first premises disconnecting means after a POCO service drop or lateral.

What you have is just a disconnect... equipment disconnect if you wish.
 
C

CJW66

Member
Location
London.Ontario,Canada
Smart $ said:
For future reference, this would definitely not be a service disconnect, which refers to the first premises disconnecting means after a POCO service drop or lateral.

What you have is just a disconnect... equipment disconnect if you wish.
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We call it a service disconnect over here in Canada. All it means is "a disconnecting means to service the equipment". Has to be in line of sight.
Also, you never did say the source that it was fed from. Ampacity I mean. If it's fed from a breaker panel, and the proper size breaker, you don't need a fusible disconnect...
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
CJW66 said:
We call it a service disconnect over here in Canada. .
Click to expand...

Yeah and you mount your panels sideways.:D

But please, this is an NEC forum and it helps us to answer the questions correctly when people use the NEC terms. :)
 
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Smart $

Smart $

Esteemed Member
Location
Ohio
CJW66 said:
We call it a service disconnect over here in Canada. All it means is "a disconnecting means to service the equipment". Has to be in line of sight.
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I realize many call it that... but it causes confusion when talking Code without specifying at least, in some manner it is the "for maintenance" or "within sight of" type.
 
C

CJW66

Member
Location
London.Ontario,Canada
iwire said:
Yeah and you mount your panels sideways.:D

But please, this is an NEC forum and it helps us to answer the questions correctly when people use the NEC terms. :)
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We only mount the panels sideways in a service upgrade. If the wires are too short. Other than that, we do things correctly over here. We don't cut corners.
 
fifty60

fifty60

Senior Member
Location
USA
From here on, I will refer to the disconnect as an "Equipment Disconnect". I appreciate the clarification.
 
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