Plugging 30 amp flexible cord into 50 amp outlet

[kwired]

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

Could be, OP never mentioned whether or not these are on wheels or if frequently interchanged in any way. So far all he mentioned is disconnects were provided for LOTO yet a cord and plug is an easy disconnect and LO procedure than a disconnect switch - especially for electrical work where you need to verify absence of voltage, if you have the cord cap in your hand and can see it is separated from the receptacle I would hope that is enough verification. Maybe they want you to put bonding jumpers across all the cord cap pins

 

[LEO2854]

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 .

Could be, OP never mentioned whether or not these are on wheels or if frequently interchanged in any way. So far all he mentioned is disconnects were provided for LOTO yet a cord and plug is an easy disconnect and LO procedure than a disconnect switch - especially for electrical work where you need to verify absence of voltage, if you have the cord cap in your hand and can see it is separated from the receptacle I would hope that is enough verification. Maybe they want you to put bonding jumpers across all the cord cap pins

The part of his post that i high lighted in red gives me the idea that they want to be able to move them around to any location but I don't know for sure unless he verifies that.

Maybe they want you to put bonding jumpers across all the cord cap pins

That would be fun...:lol:

 

[Davebones]

Yes these a portable . They set up hydraulic lines into the chambers and cycle the parts inside to see how they work under high and low temperature . They might do up to a million cycles and then break down the test set-up . The chambers do get moved around depending upon which test stand needs a CSZ ( Hot & Cold Environment ) .

 

[thunder15j]

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 .

As per table 400.5(A) column A (3 current carrying conductor cords) #10-4 SO cord has an ampacity of 25 amps. And continuous duty rating is not even in the equation. Just missed the cut. Looks like #8-4 cord @ 35 amps should be used.

 

[zbang]

Well, 240.5 says:

240.5 Protection of Flexible Cords, Flexible Cables, and Fixture Wires. Flexible cord and flexible cable, including tinsel cord and extension cords, and fixture wires shall be protected against overcurrent by either 240.5(A) or (B).

(A) Ampacities. Flexible cord and flexible cable shall be protected by an overcurrent device in accordance with their ampacity as specified in Table 400.5(A) and Table 400.5(B). Fixture wire shall be protected against overcurrent in accordance with its ampacity as specified in Table 402.5. Supplementary overcurrent protection, as covered in 240.10, shall be permitted to be an acceptable means for providing this protection.

Nothing in (B) applies to this case. As I read it, if the 50a receptacles are fed by 50a breakers, then the cords must be rated for 50a regardless of the load.

And I don't think we can't hang our collective hat on 240.10:

240.10 Supplementary Overcurrent Protection. Where supplementary overcurrent protection is used for luminaires, appliances, and other equipment or for internal circuits and components of equipment, it shall not be used as a substitute for required branch-circuit overcurrent devices or in place of the required branch-circuit protection. Supplementary overcurrent devices shall not be required to be readily accessible.

 

[LEO2854]

Well, 240.5 says:


Nothing in (B) applies to this case. As I read it, if the 50a receptacles are fed by 50a breakers, then the cords must be rated for 50a regardless of the load.

And I don't think we can't hang our collective hat on 240.10:

I do not agree , the cords are going in to fused disconnects with 30 amp fuses so the cords are protected from over current.

 

[kwired]

Well, 240.5 says:....

240.4 says some of the same things but applies to conductors other than flexible cords. It does mention tap conductors in subpart E. 240.5 that covers flexible cords does not mention tap conductors at all. I would think this means the ampacity of the cord in the OP case needs to be 50 amps.

 

[Davebones]

Looking at table 400.5 ( A ) ( 1 ) I see it does say allowable ampacity for # 10 SO cord in column " A " is 25 amps . We have the fusible disconnects fused at 25 amps with no problems .

 

[Davebones]

240.5 Would ( B) ( 1 ) not apply ? " SUPPLY CORD SHALL BE CONSIDERED TO BE PROTECTED WHEN APPLIED WITHIN THE APPLIANCE " ???

 

[zbang]

If you're attaching a shop-made cord, then it isn't:

240.5(B)(1) Supply Cord of Listed Appliance or Luminaire.
Where flexible cord or tinsel cord is approved for and used with a specific listed appliance or luminaire, it shall be considered to be protected when applied within the appliance or luminaire listing requirements. For the purposes of this section, a luminaire may be either portable or permanent.

There's also the basic concept that overcurrent protection applies "downstream", not "upstream" except in limited cases, and I don't think this is one. I don't see anything in either 240.4 or 240.5(B) that would apply to this situation.

 

[jumper]

I do not agree , the cords are going in to fused disconnects with 30 amp fuses so the cords are protected from over current.

If a cord shorts out/ is over loaded before the fuses, how does the fuses protect the cord?

 

[PetrosA]

If a cord shorts out/ is over loaded before the fuses, how does the fuses protect the cord?

There are two things you mention here:

1 - The cord being overloaded. That can only happen from the load, which is fused per the cord's ampacity rating.

2 - Shorting out the cord. The cord's current rating applies to non-fault loads. No cable is rated or fused for the potential short current it might be subjected to. Even if you ran 350 MCM CU to the unit from a 50A plug and there was a short between the plug and appliance, the wire is not rated for the available fault current it will be subjected to.

 

[LEO2854]

If a cord shorts out/ is over loaded before the fuses, how does the fuses protect the cord?

If the cord shorts out then you would hope that OCP feeding would trip because of the short;Right.


If the cord is over loaded then the 30 amp fuses in the disconnect on the unit would trip.

 

[zbang]

Perhaps I'm being dense today (this happens), but other than taps and service conductors, where in the code are you allowed to protect conductors at the utilization end?

210.20(B) Conductor Protection.
Conductors shall be protected in accordance with 240.4. Flexible cords and fixture wires shall be protected in accordance with 240.5.

and we've already been to those sections. I took a quick look in 422 (Appliances), but don't see anything applicable there, either.

BTW, in the grand scheme of things, in practice I don't think the OP's concern is much of a problem. Doesn't make it fully code compliant.

 

[jumper]

Perhaps I'm being dense today (this happens), but other than taps and service conductors, where in the code are you allowed to protect conductors at the utilization end?

210.20(B) Conductor Protection.
Conductors shall be protected in accordance with 240.4. Flexible cords and fixture wires shall be protected in accordance with 240.5.

and we've already been to those sections. I took a quick look in 422 (Appliances), but don't see anything applicable there, either.

BTW, in the grand scheme of things, in practice I don't think the OP's concern is much of a problem. Doesn't make it fully code compliant.

Well, I am just as dense as you on this, 'cause this what I was trying to say.

 

[kwired]

Perhaps I'm being dense today (this happens), but other than taps and service conductors, where in the code are you allowed to protect conductors at the utilization end?

210.20(B) Conductor Protection.
Conductors shall be protected in accordance with 240.4. Flexible cords and fixture wires shall be protected in accordance with 240.5.

and we've already been to those sections. I took a quick look in 422 (Appliances), but don't see anything applicable there, either.

BTW, in the grand scheme of things, in practice I don't think the OP's concern is much of a problem. Doesn't make it fully code compliant.

Going back to my post in #27:

240.4 says some of the same things but applies to conductors other than flexible cords. It does mention tap conductors in subpart E. 240.5 that covers flexible cords does not mention tap conductors at all. I would think this means the ampacity of the cord in the OP case needs to be 50 amps.

Tap conductors are mentioned in 240.4 part E and that is where we are given permission to exceed the ampacity of a conductor as long as we meet the tap rules. That is for conductors in general.

Next section 240.5 which is for flexible cords does not even mention tap conductors as an exception to overcurrent protection rules. Based on this I don't believe a flexible cord is allowed to be protected above its ampacity (as a general rule - there could be exceptions). I guess I am asking you to find the exception that applies here, otherwise the cord needs protected at its rated ampacity.

 

[zbang]

kwired- we agree on this. I'm asking whoever thinks that using a fuse on the utilization equipment to protect the flex cord supplying it provide their citation that it's compliant. I don't think they'll find one.