UL and reduced capacity

[ruud-man]

I have a contractor who has installed an air handler with electric heat. He needs to reduce the heat capacity to be compatable with the existing power wiring.

Of course this can be accomplished by disabling one or more banks of electric heat.

My question- Has anyone here dealt with something like this and what UL implications are involved?

I have researched the I&O manuals, OEM website, and the UL website. No luck. Hope someone here can.

Thanks...

[tecman]

I don't believe that UL has any say on a matter like this. Disabling a bank would not have an impact on safety.

The other thing to consider is to run the resistance off of 120V instead of 240V. This will give you 25% of the rated wattage. If it is a separate circuit for the resistance, just put in a single pole breaker and connect the other leg to neutral. Just make sure that the hot side is connected to the sequencer, and jump out any fuse on the neutral leg to meet code. If it is a common circuit for the blower and resistance, you would need to replace the wire with a 3 conductor so you have the neurtal leg.

paul

[ruud-man]

I'm inclined to agree. Here is the rest of the story-

Plan/spec job

Arch/engineer approves an equal for Trane A/C w/electric heat.

KW ratings of equal do not match the Trane specs.

Electricians wire from prints for Trane specs.

Equal is over amperage of wiring if not derated.

Arch/Eng wants contractor to re-tag air handler as modified and not UL listed.

I've been asked to determine if indeed UL is voided.

Any ideas?

[pecmsg]

Ruud-Man
You make any changes to the heaters that are used and the package is no longer UL Rated.
From your post I suspect that either the breaker is tripping or the Electrician is claiming it will trip. You only have 2 options.
1) Remove and replace the electric heaters with a lower KW rating
Or
2) Have the electrician increase wire gauge and breaker.


tecman,
Don’t play with electric. If you cut your voltage in 1/2 you double your amperage.


[Edited by pecmsg on 06-02-2005 at 04:11 PM]

[ruud-man]

Thanks for the info.

My reasoning is there will be no change to the number nor size of the banks. All the components are intact.

Basically, the contractor wants to disconnect a bank so it never energizes.

Actually, I beleive the A/E dropped the ball by not catching it in the submittal process.

But, as you know, they (A/Es) never make a mistake.

Thanks again...

[dash]

Originally posted by pecmsg
Ruud-Man
You make any changes to the heaters that are used and the package is no longer UL Rated.
From your post I suspect that either the breaker is tripping or the Electrician is claiming it will trip. You only have 2 options.
1) Remove and replace the electric heaters with a lower KW rating
Or
2) Have the electrician increase wire gauge and breaker.


tecman,
Don’t play with electric. If you cut your voltage in 1/2 you double your amperage.


[Edited by pecmsg on 06-02-2005 at 04:11 PM]

Correct,and in our area they would red tag it if noticed.

[Reliant Air]

Originally posted by ruud-man
Thanks for the info.

Actually, I beleive the A/E dropped the ball by not catching it in the submittal process.

But, as you know, they (A/Es) never make a mistake.

Thanks again...

And your contractor is perfect.

This is probably what would have happened if it was my job. I would have accepted substituted equipment, but I would have know that there were changes to the electrical requirements. I would have gave the submittals to the electrical engineer and told him to find any changes. He would make note of the changes and look for them when he inspects the job. The submittals would be returned with a comment like this.

Coordinate any changes to the electrical requirements with the electrical contractor. The mechanical contractor shall accept any additional costs associated with new electrical requirements due to the substituted equipment.

My guess is that the engineer was looking for this because there was a substitute for the equipment and it ended up on a punch list. Now the mechanical is trying to get out of paying for the electrician to pull new wires and increase the breaker size because he didn't coordinate the changes. Perhaps the engineer is going to accept a smaller KW, and the contractor still wants to be cheap and rig it up to work.

Of course I don't know this just like you didn't know that it's the engineer's fault. This issue is so common that the engineer would have to have less than 6 months experience to not know that the electrical requirements would change with substituted equipment. It's not our responsibility to redesign everything just so a contractor can save a few bucks.

BTW the UL listing is voided if the product is modified. and MOC is based on specific equipment combinations. You might prevent nuisance trips by butchering the heat strips, but you will never find manufacturers data to document the correct size.

[tecman]

Originally posted by pecmsg


tecman,
Don’t play with electric. If you cut your voltage in 1/2 you double your amperage.


[Edited by pecmsg on 06-02-2005 at 04:11 PM]

Sorry but I need to correct you. For a resistive load, I=E/R

Since the resistance of the element is a fixed value, the current is 1/2, and with the voltage is 1/2, the power is 1/4 (P=E*I, or P=E^2/R. Current only goes up as voltage drops with some non-linear devices, like some types of motors.

It is not "playing" with electrics. No changes to the heater is required.

BTW I do have a BS in electrical engineering as well as being a licensed electrician.

paul

[beenthere]

Just disable the last bank. Then mark it as the arc said, and note, that you did this as per his instructions.

OR, just order in the correct size strip package.

[pecmsg]

Originally posted by tecman

Originally posted by pecmsg


tecman,
Don’t play with electric. If you cut your voltage in 1/2 you double your amperage.


[Edited by pecmsg on 06-02-2005 at 04:11 PM]

Sorry but I need to correct you. For a resistive load, I=E/R

Since the resistance of the element is a fixed value, the current is 1/2, and with the voltage is 1/2, the power is 1/4 (P=E*I, or P=E^2/R. Current only goes up as voltage drops with some non-linear devices, like some types of motors.

It is not "playing" with electrics. No changes to the heater is required.

BTW I do have a BS in electrical engineering as well as being a licensed electrician.

paul

If you say so!!!

[cem-bsee]

I say so, too

One only voids the warranty when one modifies a listed unit.

Any lawyer would have to walk on water in front of the Judge to prove that disconnecting a wire, or removing an individual heat strip fuse was a modification! IMO.

In fact, this makes the unit SAFER!

[beenthere]

wrong thread.

[ruud-man]

Thanks for all the input. Sounds like I may have offended an engineer out there. No offense intended. That was a generaliaztion that was out of line.

But, I have to share this. The contractor asked me to contact the A/E and assure hime that we were providing electric furnaces that were 100% efficient. It seems he was told that the equipment was a builders model that was using inefficient heater banks.

I pretty much fiqured if I lived long enough I will have heard it all. That one was pretty close.

Anyway, here is more of the story. It seems the specified power service for the building will not support the added KW of the furnaces.

For the record, I personally don't advocate any modification to heating equipment, but I promised the contractor I would research it.

Thanks again for your replies.