Non Fusible Disconnect Higher Amp than CB

[killer76]

I have a application were the designer has a 30 amp Non Fusible Disconnect as a safety disconnect for a 20 amp A/C fead from a 20 amp circuit breaker

I feel that the Non Fusible Disconnect should not be higher than the supply circuit breaker

I have not been able to find an exception in the code,

Thanks
Robert

 

[charlie b]

Re: Non Fusible Disconnect Higher Amp than CB

There is no reason that it can't be a 100 amp disconnect. The rating of the disconnect is simply a statement, by its manufacturer, of the minimum current it can handle without sustaining damage. This one is not used for overcurrent protection, so it's having a higher rating than the fuse means nothing.

 

[stud696981]

Re: Non Fusible Disconnect Higher Amp than CB

If I understand your question correctly, the disconnect box you have is fine. A disconnect box has to meet or exceed the rating of the circuit. So in this case you have a 20A circuit but a 30A box, no problem.

A non-fused disconnect provides NO over current or short circuit protection, so you simply want to have one rated at or above the circuit in question.

 

[stud696981]

Re: Non Fusible Disconnect Higher Amp than CB

Sorry, looks like Charlie beat me to it.

 

[steve66]

Re: Non Fusible Disconnect Higher Amp than CB

I feel that the Non Fusible Disconnect should not be higher than the supply circuit breaker

It's basically the opposite. The disconnect must be at least as large as the supply circuit, as Charlie B. pointed out. And 30A is pretty much the smallest standard size for a disconnect.

Steve

[ August 30, 2005, 11:58 AM: Message edited by: steve66 ]

 

[infinity]

Re: Non Fusible Disconnect Higher Amp than CB

I feel that the Non Fusible Disconnect should not be higher than the supply circuit breaker

Maybe it's me, but I'm slightly bothered by an "Electrical Designer" who would ask this question.

 

[charlie b]

Re: Non Fusible Disconnect Higher Amp than CB

Originally posted by infinity:Maybe it's me, but I'm slightly bothered by an "Electrical Designer" who would ask this question.

I'm not. But I may have a different understanding of that phrase.

To me, an "Electrical Designer" is a person who started their career as a drafter. As their career progressed, they would be assigned to both lay out electrical devices and to perform the CAD work. Eventually, the person would be doing complete design packages, under the supervision of a PE.

But the term "Electrical Designer" does not tell us how much of the design process the person has yet learned. It is like describing yourself as an "electrician." That word does not tell me whether you are a first year apprentice or a Master who is nearing retirement.

Even so, a Master and a PE have one thing in common: neither has yet learned it all.

 

[rick hart]

Re: Non Fusible Disconnect Higher Amp than CB

Are there any 20 A NEMA rated A/C disconnects out there? I thought 30A was where they started.....

 

[jimwalker]

Re: Non Fusible Disconnect Higher Amp than CB

Why not simply use a $10 pull out 60 amp disc.Cheap,easy to install,code compliant

 

[hurk27]

Re: Non Fusible Disconnect Higher Amp than CB

Are there any 20 A NEMA rated A/C disconnects out there? I thought 30A was where they started.....

Yep: