ECN Forum Forums Code Related Discussion NEC & other Code issues Whaaat size disconnect?

Thanks Don, you and I and so many others really benefit from interacting on this BB, it caused us to compare notes as it were and dig out the old code book. I have had to change my thinking more than once- listening to you, Bob, Roger and the rest so let's keep it going.

George

I've read the section about 30 times. I see what you are getting at George. I agree.

I saw a 30 amp disco, DU221RB, rated at 3 HP.

I still have a question though. Is the intent of 440.12(B) [and 430.110(C) for that matter] trying to say 'figure the HP rating twice(using the motor tables), both by the rated current of the motors and by the locked rotor current of the motors; whichever is the highest HP rating figured is the required rating of the disco?

If that's what is suppose to be done, it doesn't say that very well. If I still don't get it--HELP!

Also, can I still use (trust) the equipment current rating or do I have to check the ampere & LR rating of the compressor and blower motors separately?

i once priced 30amp and 60 amp disconnects and got a better price on the 60 amp one.

I went out and looked at the label of my Trane and the LRA is 91a. How does that relate to disconnect size?

Greg- 91a. would equate to 3 HP per Article 430 T. 430.251(A). I have a 60a. fused switch in the garage that is labeled 3 HP using Standard fuses and 10 HP Maximum. My understanding is that Standard fusing is one time fusing and Maximum is using time delay. (hope I don't have that backwards).

Thanks, that is what I believed but it is good to hear someone else say it.

I ended up with a 60a rated disconnect too since the breaker in it is 40 (per the O/C device spec on the label).

In a disconnect without O/C protection I agree with those who say you will need one that is HP rated, like any other disconnect. I fear a "30" might be aimed at water heaters if it is not specifically labelled with a HP rating. If it is thusly labelled, go by the label. I am sure most pullouts can open LRA but you should be wearing gloves and sunglasses

Hard to beat $8 for a 60A NEMA-3 HVAC disconnect regardless of what ampacity or use. Mass production and economy of scale does have SOME advantages!