Thread: 240-volt versus 208-volt

Confused by lack of knowledge on where/when you have 240-volts or 208-volts:

See attached nameplate on a 2005 heat-pump air handler. The unit had a 35-amp OCD. The minimum s/b 37A (in essence a 40A) for 240v or 32A (in essence a 35A) for 208v. The maximum s/b 40A for 240v and 35A for 208v.

How do I know which applies (240v o 208v)?
This unit is either correctly matched with a 35A, or under-fused and should have a 40A (for the 37A min.).

Dave

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You would have to know what the supplied voltage is to circuit.

And HOW does one learn or know what that is ???
Do you have to 'test' each instance or is a local/regional power utility standard?

Test it, it depends on the transformer selection from the power company. Most but not all residential in my area is 240.

Every clothes dryer receptacle I've tested has been 240-volt.

208 volts will generally be derived from a 3-phase system by being across any 2 of the three phases.

Residential is typically 120/240

208 is 3-phase. You won't generally find 208 in residential, especially regular houses, at least not around here. 3 phase is mostly for commercial, industrial. The rating plates on the motor are written that way because the motor can be used on a 3 phase system. The difference ends up being how you attach the incoming legs to the motor terminals.
I did do a 4 unit res condo conversion years ago where we installed 3-phase just to run the elevator.
How is your utility distribution down there? We have utility poles in the alleys that the electrical wires run on to feed the houses. If one looks at the poles, there is usually one transformer (big round thing) mounted on at least one pole on each block. In order to have 3-phase you need two or more transformers on the same pole (according to the utility guys).

Thanks Michael.
So this is wrong and does not meet the manufacturer's minimum circuit ampacity requirement.

Originally Posted by Dave Hahn

Thanks Michael.
So this is wrong and does not meet the manufacturer's minimum circuit ampacity requirement.

The maximum breaker size is stated as 40(240V)/35(208V) So your 35A is OK for either 240 or 208.

The circuit ampacity is not determined by the breaker size.

If there is no nuisance tripping, I don't think I would have a problem with it from the information you have provided.

Circuit ampacity would be determined by the wire gauge.

Originally Posted by Dave Hahn

Circuit ampacity would be determined by the wire gauge.

Yes it is.

Originally Posted by Dave Hahn

See attached nameplate on a 2005 heat-pump air handler. The unit had a 35-amp OCD. The minimum s/b 37A (in essence a 40A) for 240v or 32A (in essence a 35A) for 208v. The maximum s/b 40A for 240v and 35A for 208v.

Dave,

That nameplate is stating that if:

- The circuit is 208 volts (some condo buildings will have 208 volts), then the *minimum* circuit size is 32 amps and the *maximum* circuit breaker size is 35 amps.

- The circuit is 240 volts, then the *minimum* circuit size is 37 amps and the *maximum* circuit breaker size is 40 amps.

Being as you did not state the circuit size, you question of whether this is correct or not cannot be answered.

All which can be stated from your information is that the 35 amp breaker size "is okay for both 208 volts and 240 volts".

Don't apply the circuit ampacity minimum to the overcurrent protection size when dealing with those name plates. There is nothing wrong with having a 40 amp rated circuit and having 35 amp breaker.

And, as shown on the line above the line marked, you could even have (if that line had been marked) a 35 amp breaker on a 31 amp circuit - all because it says so on the nameplate. Go up to the top line (labeled 'None') and you could even have a 15 amp breaker on a 5 amp rated circuit.

Gerry, other than a shot at the last post in the thread, just what new information did you add to this conversation?

Originally Posted by Michael Larson

Gerry, other than a shot at the last post in the thread, just what new information did you add to this conversation?

Who's "Gerry"?

Michael,

Like it or not (I am presuming you are referring to my post as I guess I am closest to "Gerry") my post was more relevant than your last post.

My post clarified, explained, and tied several things from other posts together in one post.

And, WTF you talking about with "other than a shot at the last post"??? There was no shot at anyone, well, other than your shot at "Gerry".

Originally Posted by Jerry Peck

Who's "Gerry"?

Michael,

Like it or not (I am presuming you are referring to my post as I guess I am closest to "Gerry") my post was more relevant than your last post.

My post clarified, explained, and tied several things from other posts together in one post.

And, WTF you talking about with "other than a shot at the last post"??? There was no shot at anyone, well, other than your shot at "Gerry".

Yes I meant you Jerry. Post away.

Michael...

Regardless of the content and/or motivation of Jerry's (or "Gerry's") response, why was your 'comment' needed, especially to a post not authored by you ?

As Jerry eloquently stated, WTF ?

Dave

Originally Posted by Dave Hahn

Michael...

Regardless of the content and/or motivation of Jerry's (or "Gerry's") response, why was your 'comment' needed, especially to a post not authored by you ?

As Jerry eloquently stated, WTF ?

Dave

I guess we both have an attitude Dave. Have a nice day.