electrical circuits and high efficiency

[classicrock4you]

High efficiency and 410a systems are creating situations where the breaker size and wire size can be smaller than the existing 15 year old R22 system.
1) Has anyone else have had an inspector say " change the wire size"?
Remember, He who proves an inspector wrong will have rejections up
the ying yang for ages.
2) What is the legal liability if the wire size is not changed and that wire is
involved in a fire?
3) What are you guys doing - change only breaker or the wire size too.

[larobj63]

There is no penalty for "oversized" wire, IMO.

The breaker needs to be the right size - which is to say it can be too large. But the wire has to be the minimum gage or larger, as far as I know.

[deckeda]

... He who proves an inspector wrong will have rejections up the ying yang for ages. ...

Maybe, but he who rejects work should be able to cite the verifiable code, yes?

larobj63 is correct.

[hvaclover]

That doesn't matter in a lot of cases. One time I called on an inspector on a bogus violation. I quoted him rhyme and verse the section allowing the what I had done.

I'll NEVER forget what he said to me, and I quote "Just because you can read the code book doesn't mean you can interpret it. You have to be an inspector".

I just shook my head and went over his to his boss.

[temco]

I cant say about legalities, Im not a lawyer, electrician or inspector.
And the following is not advice. Confirm with your job site inspector.
Does your existing system have a fused disconnect?
The breaker needs to be sized to protect the wire. You cant install a 40 amp breaker on a circuit with 60amp rated wire. The unit needs to be protected by properly sized fuses and or breaker. If you dont use a fused disconnect you will have to change the breaker and wire.
If I have an existing 60amp breaker with #6 wire and a fused disconnect with 60amp fuses, and my new unit requires a 40amp fuse or breaker. I reuse the existing 60amp breaker and wire up to the disconnect. Install new 40 amp fuses and run #8 wire from disconnect to unit. (#6 wire is protected by 60amp breaker and unit and #8 wire is protected by 40amp fuses).

[bobRitchie]

The idea that the wire has to be made smaller is ridiculous.
Dropping the breaker/ and fuse sizes to protect the equipment may
be necessary. There is no upper constraint on the wire size, it
just needs to be large enough to prevent excessive IR drop.
I work in software but am a MSEE. Just think of the many examples
of huge wires with little current. Your whole house service wire with
nothing but a few clocks and electronic stuff in sleep mode... Your
range with one small burner on low...

No problem with a small current in a big wire.
Now a big current in a small wire means heat IR drop ... lots
of trouble.

[diverdan]

If an inspector would call me on amperage I'd just change the breaker size and leave the wire supply alone. You CAN take a 2 pole 30 amp circuit and change the breaker out to 2 pole 20 amp and leave the wire size at #10 rather tan replacing it with #12. You can oversize the conductor without a problem. Just keep the over current protection correct.

[temco]

Yeah no problem with smaller current in a larger than necessary wire. Its a matter of code. Cant have a breaker that is not large enough to protect the wire size at its largest rated current. Reqardless of the actual load.
(of course ive been wrong once or twice before). Confirm with your inspector or NEC.

[temco]

I was out in the garage and realized I was describing this backwards as far as the breaker needing to be rated high enough rather than low enough to protect the wire. Have to retract what I said (looks like I was wrong for the third time this year).

[hvaclover]

Remember that one thing/lesson that happenens to everyone in hvac school that you never forget.


We were teraring down equip and cataloging each compoment by the data.

The unit I was working on was a 110v window shaker and I had removed a selector switch. I went to my instructor and told him the switch was no good for the wondow shaker. He asked why and I said it was rated at 220 vac and the window shaker is only 110v.

The instructor smaked me in back of the head .

Lesson learned Mr. Umstadt.

[larobj63]

I was out in the garage and realized I was describing this backwards as far as the breaker needing to be rated high enough rather than low enough to protect the wire. Have to retract what I said (looks like I was wrong for the third time this year).

Very nice.

I was about to attact your first post like a spider monkey before I read this one... :)

I kid, I kid...

[beenthere]

The wire is sized by both amp draw, and voltage drop.

You could have a max protection 30 amp device circuit that needs #6 wire because of length of run to prevent excess voltage drop, and the circuit would still use a 30 amp breaker.

[wraujr]

Now wait a minute...

You can replace a 110 switch with a 220 switch, but I can't replace a 170 limit with a 220 limit (see other post).. Why?? the numbers are both higher....

Is this why pros are reluctant to give DIY advice???

[beenthere]

Now wait a minute...

You can replace a 110 switch with a 220 switch,

Yes, that is completely safe.


but I can't replace a 170 limit with a 220 limit

No, that would be entirely UNSAFE

(see other post).. Why?? the numbers are both higher....

The one is just a switch device, the other is a safety device.

Is this why pros are reluctant to give DIY advice???

Yes. DIYers don't know what is and is not safe. Or fully understand what a part/device does, and will make assumtions that if going bigger with one thing is ok, then it is ok with the next thing.

When it isn't.

[larobj63]

Yes. DIYers don't know what is and is not safe. Or fully understand what a part/device does, and will make assumtions that if going bigger with one thing is ok, then it is ok with the next thing.

When it isn't.

He was just joking... :)

That's why pro-members aren't stand up commics. :D

[beenthere]

He was just joking... :)

That's why pro-members aren't stand up commics. :D
:)

[DanW13]

If you look hard enough there's charts to read across the web and maybe in some of your tool manuals that will tell you what gauge wire is need for a spefic lenght of extension cord, thus the same type of rating is applied to gauging wire for electrical runs. But when it comes to breakers you need to have the proper size breakers no matter what gague wire is used to protect the equipment from over heating and creating a fire hazard.

[MRcoolingMAGIC]

There is no penalty for "oversized" wire, IMO.

The breaker needs to be the right size - which is to say it can be too large. But the wire has to be the minimum gage or larger, as far as I know.

Absolutely correct.The bigger the wire the easier the current travel in less resistance and no overheating occurs.:D

[cem-bsee]

if one has a disconnect at the end of the wire with the proper overcurrent, that is per NEC & safe! -- fuse or breaker in disconnect.

one could have a #2 wire and 100a bkr in panel, and 30a disconnect with 25a Fusetrons beside compressor needing 20a --

[hvaclover]

Code here requires us to have the ac fused at the disconnect and fused/breaker at main of proper size to suit the ac tonage.

[DanW13]

if one has a disconnect at the end of the wire with the proper overcurrent, that is per NEC & safe! -- fuse or breaker in disconnect.

one could have a #2 wire and 100a bkr in panel, and 30a disconnect with 25a Fusetrons beside compressor needing 20a --

How does a 25 or 30 amp breaker protect a 20 amp compressor ? :rolleyes:

[beenthere]

How does a 25 or 30 amp breaker protect a 20 amp compressor ? :rolleyes:
Motor only load is allowed to have a larged then name plate rating breaker.

[larobj63]

Motor only load is allowed to have a larged then name plate rating breaker.

Yup. Without getting too specific, a motor can draw several times its RLA during start-up, but only for a split second. Breakers use an inverse time function...

I believe motor loads are usually overcurrent protected at 125% RLA -

[wraujr]

You stated "How does a 25 or 30 amp breaker protect a 20 amp compressor "

It doesn't. A circuit breaker or fuse is intended to protect the circuit that distributes the electricity (i.e. wire), not the actual load (i.e. compressor). If a compressor draws too much it has failed and the circuit breaker can't help it. But, the CB can protect damage to wire, etc.. or and did I mention fire.

For What its Worth, its very interesting to look at the response curves of a conventional circuit breaker to see how fast it may respond to various over currents. With a 20 amp breaker and 21 amps it may take anywhere from 300 or more seconds (yes, thats 5 minutes) to trip. At 30 amps, its 20 to 125 seconds. At 60 amps, its 3 to 10 seconds. Bottom line is circuit breakers trip fast for shorts, etc.

[larobj63]

For What its Worth, its very interesting to look at the response curves of a conventional circuit breaker to see how fast it may respond to various over currents. With a 20 amp breaker and 21 amps it may take anywhere from 300 or more seconds (yes, thats 5 minutes) to trip. At 30 amps, its 20 to 125 seconds. At 60 amps, its 3 to 10 seconds. Bottom line is circuit breakers trip fast for shorts, etc.

That's the inverse time function I mentioned. The greater the amperage, the shorter the "toleration" from the breaker. A short has a resitance of zero, breaker trips immediatly...

Just expanding on what you said, not correcting, you are right...