Unconventional HVAC installation

[bphgravity]

I have a single family home with a 5 kw air handler and a 30A max, 23A RLC a/c unit. The blower motor in the air handler is 1/4 hp, 2.7A.

The contractor installed a single 30A branch circuit to serve both the a/c and a/h. The branch circuit originates in the L&A panelboard as #6 to a junction box in the attic. From that location they ran a #10 to the a/c unit and a #6 to the a/h. There is appropriate disconnecting means for each unit.

Anyone have an issues with this setup?

 

[petersonra]

Re: Unconventional HVAC installation

it seems to me like it might be overloading the circuit which might well cause the 30A CB to trip, but I don't see any code violation.

 

[macmikeman]

Re: Unconventional HVAC installation

I bet it will run without overcurrent trip of the circuit breaker. For this unit, even with rla of 23 amps on the nameplate, if you amp test it while running, you will probably get a reading of around 12 amps on each leg. When this machine gets old and startups are harder, then you might see some startup tripping issues.

 

[augie47]

Re: Unconventional HVAC installation

If the L&A panelboard breaker is 30 amp (I assume it is since you identified it as a 30 amp branch circuit)..i see no code problem.

 

[infinity]

Re: Unconventional HVAC installation

I bet it will run without overcurrent trip of the circuit breaker. For this unit, even with rla of 23 amps on the nameplate, if you amp test it while running, you will probably get a reading of around 12 amps on each leg. When this machine gets old and startups are harder, then you might see some startup tripping issues.

How can a unit with a RLC of 23 amps on the nameplate only draw 12 amps?

 

[suemarkp]

Re: Unconventional HVAC installation

I hope this is an air conditioner and electric heater, not a heat pump. If the heat and cool don't run at the same time, you're probably fine. The compressor circuit is real tight, since you need RLC*1.25 + blower motor amps. If the RLC is a combination fan and compressor, then you may just squeak by at 30 amps.

If this is a heat pump, you'll trip the CB when it defrosts or it is so cold out that the compressor and strip heat run at the same time. But it is possible to configure heat pumps to not use the strip heat during defrost and to lock out the supplemental strip heat. I just don't think most people are happy when that has been done.

 

[rhurey]

Re: Unconventional HVAC installation

Originally posted by infinity:
How can a unit with a RLC of 23 amps on the nameplate only draw 12 amps?

Mine does. Two stage unit so runs stage 1 most of the time @ 8A. Runs stage 2 @ 12A. FLA's 22A IIRC.

The full load is also a function of the pressure the unit needs to create, and varies based on all kinds of thermal factors. My heat pump draws LESS current the colder it gets outside when run in heat mode. I've never used it to cool, so I can't comment on that.

 

[bphgravity]

Re: Unconventional HVAC installation

Let me give you some background information so you can undertand the concern out of my office. On the first inspection, the installation was actually a 60A feeder to a 60A sub panel at the aire handler location. From that point, 2-30A branch circuits served both the a/h and a/c. The job was failed for inaccessibility and lack of proper working space for the disconnect. (It was installed in the air handler closet and was covered by the unit)

On second inspection, the 60A breaker was removed from the L&A panelboard and replaced with a 30A breaker and a lock-out device. Over at the a/h closet, the disconnect panel was removed. This is when we discovered the contractor changed the 60A feeder circuit to a single 30A branch circuit for both loads.

Upon descriping this entire event to my director, it became his decision that the job was not acceptable and the only options we would allow them would be to either install two indivdual branch circuits for each unit, or make the original circuit a feeder again and simply place the disconnect panel in an accessible location.

The main concern is that the 30A breaker in the L&A panelboard could be changed in the future to a higher rating if the heater unit or a/h is upgraded. Meanwhile, the #10 tapped into this circuit becomes overfused. Its a weak arguement, but thats what the office concensus is.

I have only two choices in this matter. I either have to force this upon the contractor without a solid code reference or violation, or I have to come up with something this weekend to convince my assoicates the installation is okay as is. A rock and a hard place if you no what I mean.

Thanks for the opinions!

 

[mdshunk]

Re: Unconventional HVAC installation

Originally posted by bphgravity:

The main concern is that the 30A breaker in the L&A panelboard could be changed in the future to a higher rating if the heater unit or a/h is upgraded. Meanwhile, the #10 tapped into this circuit becomes overfused. Its a weak arguement, but thats what the office concensus is.

I'd be a little upset at you if you failed me for a violation that has not occurred yet, but someone might do in the future.

 

[bphgravity]

Re: Unconventional HVAC installation

Originally posted by mdshunk:
I'd be a little upset at you if you failed me for a violation that has not occurred yet, but someone might do in the future.

I am already aware of how the contractor is going to feel about this issue. That is not the point. The purpose for the discussion is to avoid anyone being upset.

 

[jimwalker]

Re: Unconventional HVAC installation

"The main concern is that the 30A breaker in the L&A panelboard could be changed in the future to a higher rating if the heater unit or a/h is upgraded. "

You can not fail him on what someone might do later.I admit your concern is warranted because someone will see the #6 wire.But often we see upsized wire because of voltage drop.

Why not ask him to tag the wire so anyone in future knows not to go over 30 amp breaker.I don't much care for his install but unless its a heat pump i believe it passes.You did not state if this was romex (nm)but i assume it is.

Using your logic you would have failed my install of an AC outside unit with max breaker of 40 amps on #6

[ September 02, 2005, 09:55 PM: Message edited by: jimwalker ]

 

[bphgravity]

Re: Unconventional HVAC installation

Its not as simple as a voltage drop conductor increase issue, though that arguement is significant. Trust me, I made it. The real issue is that this is not what the contractor every intended to do in the first place. It is a band-aide solution that my office does not like. This is not a case where this contracotr plans on performing this on the next 100 jobs. What happened here was a minor violation that resulted in the contractor making a fix that is questionable to say the least.

Is this a dis-service to the homeowner that is buying the home? I say yes.

Does this make servicing or maintenance to the units confusing and inconvient? I say yes.

Does this NOT allow for future adequecy and expansion? I say yes.

Are those opinions code solid arguements that can be enforced by the inspector. Definetly no. But if the only things you guys can give me is that not allowing you to do this specific installation will make you upset, or that you don't have to worry about what might happen later, I am not going to be able to pass this job. That's for sure.

I need to come up with something way more substantial than that in order to convince my office that a/h and a/c don't require individual branch circuits regardless if they are noncoincidental or loads that can be served by one circuit. You see what my problem is?

 

[jimwalker]

Re: Unconventional HVAC installation

Yes i see your problem and agree its a cheap fix to a screw up.Can you legally reject it with no code to back you up ? It's a safe install as long as no one ups the breaker.But that applies everywhere.What if someone changed a 15 amp breaker to a 20 because they keep tripping a lighting circuit ? You could not require only #12 wire to prevent this.You also can not stop someone from running all lighting circuits on #10 and fusing them at 15.True someone that is not qualified might someday put a 30 amp breaker in.Nec does not cover what if's.So far you have not sited any code to fail him on other than you don't like it.Well few here would like it or install it but it seems legal.Very poor design.I think your forced to pass this.A smart EC would try to work something out with you that both can live with.I assume he will be wiring more home in your area and it's best if you get along.Would it be a major problem for him to run a sperate feed to either the AC or air handler ? How did this get passed the rough ?

"I need to come up with something way more substantial than that in order to convince my office that a/h and a/c don't require individual branch circuits regardless if they are noncoincidental or loads that can be served by one circuit. You see what my problem is? "
How about this----tell your office he has commited no code violation.They are not required to be seperate circuits.A package unit has both on one.Should they both somehow come on it will trip the breaker yes.Actually that is ideal.Can you imagine the bill if a 5 kw is trying to beat a 3 ton.Did see this happen at a private club we go to.The AC was working it's butt off but the house got warmer.I disabled the heat contactors till next morning.

[ September 02, 2005, 11:12 PM: Message edited by: jimwalker ]

 

[pierre]

Re: Unconventional HVAC installation

Bryan
It sounds as though you have a "tap conductor" situation here. Does this setup conform to 240.21(B)(1) or (2) ?

 

[tx2step]

Re: Unconventional HVAC installation

Originally posted by pierre:
It sounds as though you have a "tap conductor" situation here. Does this setup conform to 240.21(B)(1) or (2) ?

Pierre, since this is being fed by a 30A CB and the smallest wire is #10, then is that #10 really a tap conductor? Or is it just part of a 30A branch circuit which has part of the wire oversized? I'm not clear on it in this situation.

Now if the CB gets changed to a 40A or 50A, then the #10 would be a tap conductor, and 240.21(B)(1) or (2) would apply? It might also be over the maximum CB size listed on the condensing unit nameplate?

If it's a feeder, then wouldn't you do a feeder calc. and size the panel CB to meet at least the minimum that the calc. calls for, and then comply with whichever tap rule applies?

Maybe one solution would be to upsize the panel CB to 50A and replace the 2 disconnects (@AHU and condenser) with fused disconnects or enclosed CB's of the appropriate ratings?

Bryan:
Does the condensing unit nameplate call for a minimum circuit ampacity? Does it have a maximum fuse or CB size listed? Is this a heat pump?

I'd probably ask the EC to show you his branch or feeder circuit load calc. to see if it's correct.

 

[macmikeman]

Re: Unconventional HVAC installation

You know, instead of replacing the circuit breaker in the future, the homeowner might just replace the unit with a larger package unit. In which case your electrical contractor has done him the huge favor of providing a prefabricated proper wire sized solution. He could abandon the air handler alltogether. On the other hand, he might just leave the whole thing alone , in which case since it meets code, your duty is to pass the installation, regardless of what your hardheaded bosses at the office say about it.

 

[iwire]

Re: Unconventional HVAC installation

I don't even get the question.

If you want to shoot this down you could fail it for a 250.122(B) violation assuming it is a cable. :roll:

 

[iwire]

Re: Unconventional HVAC installation

Originally posted by bphgravity:
Upon descriping this entire event to my director, it became his decision that the job was not acceptable

This director has find a code article to cite or live with it.

No?

Just a question here.

Would the 10 AWG be to small fed by a 50 amp breaker if the MCA of the unit the 10 AWG feeds is less than 30 amps?

440.3(A), 430.62(A) etc.

 

[bphgravity]

Re: Unconventional HVAC installation

I don't want to reject any job or any contractor, this is why I have brought the issue here. I'm still a licensed contractor and can perform work in other jurisdictions if I desire and would certainly not appreciate an inspector failing a job that is compliant with the NEC. At the same time, I don't ever make installations that throw up red flags.

There has been nothing brought up in this discussion that I have not already considered or addressed with my associates other than the heat pump issue. I honestly don't know, but don't think the outside unit is also a heat pump.

I have managed to avoid any heated issues for quite awhile now considering my involvement in the community. Considering I inspect in one city, contract in others, teach for the apprenticeship program and provide CEU classes to the contractors, I don't know how a conflict has not arised.

Thanks for all the help.

 

[pierre]

Re: Unconventional HVAC installation

"Considering I inspect in one city, contract in others, teach for the apprenticeship program and provide CEU classes to the contractors, I don't know how a conflict has not arised."

A conflict has not occurred because you are ethical, concerned, and honest, - not to mention you have a keen sense of what is actually happening in our great industry.


Tx2step
you are correct, the 30 ampere device slipped by me.
Thanks