240.6(A)

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anbm

Senior Member
Location
TX
Occupation
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NEC 240.6(A) listed 1, 3, 6, 10 A fuse rating.
If we have 3-phase non motor load consumes 2A,
I assume we can protect it with a local 3A fused
disconnect switch and 3#12 wires. Which section
of code requires min. fuse size to be same size
as wire size (15A) feed it? I know there is one but
couldn't find it. We ran into this before. Thank you.
 
anbm said:
NEC 240.6(A) listed 1, 3, 6, 10 A fuse rating.
If we have 3-phase non motor load consumes 2A,
I assume we can protect it with a local 3A fused
disconnect switch and 3#12 wires. Which section
of code requires min. fuse size to be same size
as wire size (15A) feed it? I know there is one but
couldn't find it. We ran into this before. Thank you.
Click to expand...

wire size has to be made for the breaker but a local fuse at a machine covers the machine, not the wire... Not sure of where in the US code it is allowed but in UK all the outlets in a residence are 13 amps, wiring is based on that with 2.5 or greater wire, and the breaker is either 20 amp or 32 amp, depending upon a ring circuit or a radial.
However, plugs are fused with as little as 1 amp and as much as 13 amp fuses, based upon the need of the appliance. During testing called PAT testing in commercial and rental accommodations you must check all plugged in appliances on a regular basis, including the size of the fuse and if it is correctly fused for the appliance.

The local, at the machine fuse is something that does more than one thing, because it allows you to pull power from a device and allows you to work on it without shutting down an area surrounding it.

The fuse you would need would be based upon start up current however, if I remember things correctly, and not on normal load.
 
anbm said:
240.4(D) won't address my question, can I used 3 amp. fuses
in lieu of 15 amp. fuses as 125% of the load is less than 3 amp.?
Click to expand...

If the equipment nameplate requires 15A fuses, I assume we have to use even the
load is less than 3A and standard fuse size can be 3A?
 
anbm said:
.... Which section
of code requires min. fuse size to be same size
as wire size (15A) feed it? I know there is one but
couldn't find it. We ran into this before. Thank you.
Click to expand...

There is nothing that says you can't protect a conductor at less than it's rated ampacity. There are rules that allow you to use a greater overcurrent protection than the rating of the wire. 240.4 covers this.
 
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