Plugging 30 amp flexible cord into 50 amp outlet

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Davebones

Senior Member
Location
North Of Tampa Fl
Have a Qualification lab that has 50 Amp and 30 amp 3 phase outlets thru-out that are used to feed different CSZ ( Hot & Cold Chambers ) with flexible cord . Small chambers rated for 30 amp circuits and larger one 40 amps . We are adding on to this area and they want to make all outlets 50 amp 3 phase so any chamber can be plugged in anywhere . Can we just change the male plug on the smaller chambers to 50 amps ? Does the SO #10 cord have to be changed to ? Is this allowed ? The chambers have a fusible disconnect located on each side 30 amp for small ones , 60 amp for large ones .
 
LEO2854

LEO2854

Esteemed Member
Location
Ma
Davebones said:
Have a Qualification lab that has 50 Amp and 30 amp 3 phase outlets thru-out that are used to feed different CSZ ( Hot & Cold Chambers ) with flexible cord . Small chambers rated for 30 amp circuits and larger one 40 amps . We are adding on to this area and they want to make all outlets 50 amp 3 phase so any chamber can be plugged in anywhere . Can we just change the male plug on the smaller chambers to 50 amps ? Does the SO #10 cord have to be changed to ? Is this allowed ? The chambers have a fusible disconnect located on each side 30 amp for small ones , 60 amp for large ones .
Click to expand...

If the cord comes out of a fuse disconnect and it plugs in then that should not be a problem because the cord would be protected by the fuses.:thumbsup:
 
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zbang

Senior Member
Location
Roughly 5346 miles from Earls Court
To clarify- the chambers have the fusable disconnects or the wall next to the outlet has the FD?

Even if the chambers themselves have fuses, they don't protect the cord since they're at the utilization end, not the supply. Practically, I don't think this is a big problem, but you're still supplying a 30a cord with a 50a circuit, and that's not allowed (unless there's an exception, like a welder).

You'll have to change out the cord for a 50a rating along with the plug.
 
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Davebones

Senior Member
Location
North Of Tampa Fl
The chambers have a fusible disconnect mounted on the side of the ( CSZ ) chamber . This was added to the chambers when we get a new one . We added these with the idea that if anyone was to work on the chamber they can be locked out at the disconnect .
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Davebones said:
Have a Qualification lab that has 50 Amp and 30 amp 3 phase outlets thru-out that are used to feed different CSZ ( Hot & Cold Chambers ) with flexible cord . Small chambers rated for 30 amp circuits and larger one 40 amps . We are adding on to this area and they want to make all outlets 50 amp 3 phase so any chamber can be plugged in anywhere . Can we just change the male plug on the smaller chambers to 50 amps ? Does the SO #10 cord have to be changed to ? Is this allowed ? The chambers have a fusible disconnect located on each side 30 amp for small ones , 60 amp for large ones .
Click to expand...

You could install 50 amp single receptacles on the 30 amps circuits. Not a great design IMO.
 
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broadgage

Senior Member
Location
London, England
In practice, 30 amp cord will be fine on a 50 amp outlet, provided of course that the load is no more than 30 amps.
I would have considered that portable appliances connected by a cord and plug are not covered by the NEC which refers mainly to fixed premises wiring.

If the appliances are purchased ready made and can be purchased with 30 amp cord and 50 amp plugs, and are UL or equivalent listed, then that is fine.
If, as sounds probable, these are custom made units, then it would seem reasonable to allow 30 amp cord on 50 amp plugs.

A "rule of thumb" for appliance cords is that they may be sized according to the load, not the circuit ampacity, but no smaller than about half the circuit ampacity.
So 30 amp cord on a 50 amp circuit OK
10 amp cord on a 50 amp circuit , no way !

No one worries about desk lamps plugged into 15 amp outlets on 20 amp circuits, the cord fitted to lamps is a lot smaller than 20 amps, yet the appliances are UL listed and considered safe to use.
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
broadgage said:
No one worries about desk lamps plugged into 15 amp outlets on 20 amp circuits, the cord fitted to lamps is a lot smaller than 20 amps, yet the appliances are UL listed and considered safe to use.
Click to expand...

And that is the key, those desk lamps are UL listed for a maximum circuit of 20 amps.

Just like I bet the units with the 30 amp plugs on them are UL listed for use on a 30 amp max circuit.

To look at this another way would it be acceptable to cut the 15 amp plug off of a desk lamp, install a 50 amp plug on it and operate it from a 50 amp circuit?
 
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Davebones

Senior Member
Location
North Of Tampa Fl
These units don't come with any cords . If you look at the nameplate they say 3 Phase , 208V , 26 amps on the nameplate .We then add the SO cord and a fusible disconnect to the units . They are portable with wheels .
 
kwired

kwired

Electron manager
Location
NE Nebraska
Davebones said:
The chambers have a fusible disconnect mounted on the side of the ( CSZ ) chamber . This was added to the chambers when we get a new one . We added these with the idea that if anyone was to work on the chamber they can be locked out at the disconnect .
Click to expand...

You can unplug it to disconnect it. You can put a lockable cover over the cord cap to lock it out if necessary.

Are the machines frequently interchanged - just trying to validate a reason to connect these machines with flexible cord in the first place.
 
LEO2854

LEO2854

Esteemed Member
Location
Ma
kwired said:
You can unplug it to disconnect it. You can put a lockable cover over the cord cap to lock it out if necessary.

Are the machines frequently interchanged - just trying to validate a reason to connect these machines with flexible cord in the first place.
Click to expand...

I think that is what they want to do move the machines around when needed.
 
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