Motor Quest. 430-42

[tryinghard]

Do you think it is possible to have a ?[UL] listed appliance? that uses a 1 ? HP motor that actually includes a ?U-Slot? [factory installed] cord end to plug into 120V general use outlets?

I was called out to trouble-shoot a case like this. The appliance is a box type exhaust fan used to evacuate air in confined spaces. The motor was cycling from heat rather than tripping the 20A breaker. It is a multi-tap 120/230V but the mechanics bought it for the convenience of the u-slot, so re-tapping is not in question. The nameplate on the motor as well as on the appliance shroud is 20.4A at 120V and the nameplate also includes the manufactures address, phone number and patent number but it does not include a UL listing number or even say UL listed.

I have directed the mechanics to buy another exhaust fan that is UL listed and I?m sure it probably wont have a motor larger that 1HP. The only option for the existing 1 ? HP will be to re-tap to 230V and change the cord & cap.

How did this exhaust fan unit get past 210-23 (1), 430-42-52 & 53? Am I missing something obvious? Does anyone have a suggestion of what kind a exhaust fan to purchase?

 

[iwire]

What is a 'u slot'?

Is that a typical NEMA 5-15P 120 volt 15 amp plug?

 

[tryinghard]

What is a 'u slot'?

Is that a typical NEMA 5-15P 120 volt 15 amp plug?

Yes also 120V 20A

 

[Dennis Alwon]

So how is it that a 20 amp cord is provided with a unit that is rated 20.4 amps. Sounds like a 30 amp circuit is needed and the mfg. needs to provide a different cord.

I had a similar problem with a Viking gas range with 2 convection ovens. The unit specs had it as a 20 amp unit with a special 20 amp plug config. We installed the plug correctly but it came to us with a 15 amp cord. We made the appliance center replace the to the correct size.

 

[iwire]

This really is not a question that has an easy answer.

The unit may not be required to be UL listed.

I agree a 20 amp receptacle for a 20.4 load is not going to work.

That said many times the cords do not have to be sized like we normally size branch circuit conductors.

Lamps with 16 AWG cords are regularly plugged into 15 or 20 amps circuits.

Range cords are often 10 AWG plugged into a 50 amp circuit.

If the unit is not UL listed I would probably just swap the plug out for a 5-30P (120 30 amp plug) and run a 30 amp circuit to it.

Table 400.5(A) tells us 12 AWG cord with two current carrying conductors has a rating of 25 amps.

 

[LarryFine]

If this is a dedicated, single-load circuit, I'd opt for 10a @240v operation over 20a @ 120v anytime, especially if the circuit is already run with 12ga wire.

 

[tryinghard]

Well these mechanics are just going to have to buy another because they are adamant about prioritizing the ability to plug into any general use outlet.

This current application with a 1 1/2HP simply cannot meet the criteria of 430-42 (B) & (C), and it certainly is over 80% of the circuit rating as per 210-23 (A)(1). I just find it amazing it made it past any form of testing before being available to sell to the public.

 

[jim dungar]

The motor was cycling from heat rather than tripping the 20A breaker.

If the problem is the motor tripping its internal thermal protection and not the branch circuit device then why are you focusing on the 20A cord?

This is a portable piece of equipment so it is not always subject to the requirements of the NEC which is for premises wiring.

Because manufacturers can build what ever they want, testing agencies can test to what ever standards they want, and end users can purchase anything they want are some of the reasons that electricians must install fixed wiring to "code".

 

[tryinghard]

If the problem is the motor tripping its internal thermal protection and not the branch circuit device then why are you focusing on the 20A cord?

This is a portable piece of equipment so it is not always subject to the requirements of the NEC which is for premises wiring.

Because manufacturers can build what ever they want, testing agencies can test to what ever standards they want, and end users can purchase anything they want are some of the reasons that electricians must install fixed wiring to "code".

I actually never did care about the cord. The premises circuit is absolutely correct as a general use 120V 20A receptacle. The amazing problem is this appliance is built wrong because if it were built correctly it certainly would not be a 1 1/2HP with a 20.4A nameplate able to connect to a general use receptacle. The mechanics thought they were getting a great deal with a large volume motor that can plug in anywhere! Now they found out they?ve been scammed. You see there is no reason to bother with any other troubleshooting the thing is an overload simply with the nameplate, therefore I don?t even care why the thermal overload is tripping instead of the OCPD.

Manufactures may not always be subject to NEC but they certainly need to be compatible to NEC or their stuff wont work!

 

[LarryFine]

You see there is no reason to bother with any other troubleshooting the thing is an overload simply with the nameplate, therefore I don’t even care why the thermal overload is tripping instead of the OCPD.

Curiousity would make me want to measure the voltage at the terminals when running, just to see if low voltage is the cause.