Read the instructions with the unit.

bus driver

There are no instructions regarding this aspect. There are instructions for wiring the internal components and instruction for sizing the branch circuits that serve, but no instructions on the method of running the branch circuits to the furnace (although, a length limit is mentioned).

The amperage draw of the unit and the overcurrent protection for the branch circuit ARE specified by the manufacturer of the furnace. Most likely it is on a label, which may be inside the unit.

That is what I just said! Did you read my whole post? I'm not asking what overcurrent protection is required. I already read that information and clearly stated that in my previous post.

I am asking about the options I have for getting the power from the Service Panel to the Furnace. I know that usually a shutoff switch is used in a box on the wall by the furnace and MC is run from the box to the furnace. In this case, the furnace has its own shutoff switch right on the side so I don't think I will need a switch on the wall. However, I am planning to run the two circuits to a wall junction box, then from there to the furnace. The question is how to get the 2 circuits, one of which requires very large wire to the single knock-out. Is there a suitable MC cable for this situation (from a wall junction box to the KO) or would it be best to use rigid conduit with the cables for the 2 circuits inside?

You can punch/drill another hole for a second connector. There is no code that says you only can use the pre-punched knockouts.

joed

The space is very tight with no room for an addional KO. That is because much of the surface where I would cut a KO is covered by the built in shut-off switches.

The wires can all share one conduit (Greenfield or thinwall) if it has enough cross section. (Not the low voltage control wires as they're not apt to have appropriate insulation.)

OR, you could use a rigid conduit nipple from the KO to an external junction box. Don't forget the bushings. Fit the j-box with whatever connectors you need. I'd say MC, Greenfield, or even thinwall should be fine where they need protection.

In my jurisdiction no disconnect switch is required at or near the electric furnace (Canadian code). Also, Flex conduit (MC) is not required at the electric furnace IF the feeder is TECK cable or IF the connection point to the furnace is more than 1.5m (6') above the floor.

are you sure it requires 2 circuits to teh handler? mine has 2 breakers built in as well, but is fed by a single circuit and then broken in two in side the handler.

why not call the HVAC guys you bought it from?

I have talked to the HVAC guys about it. He said I may be able to run a single higher current conducter and split in the furnace. But, since that didn't make sense to me and because I know that they are HVAC installers, not electricians, I thought I would get a second opinion.

If I tried to run a single cable, then I would have a single cable carrying current for multiple circuits. Isn't that against code? If I had a single circuit (one breaker), that would seem to violate the requirement of separate branch circuits for the heating element and the blower/transformer.

davidandkasie
How exactly is your single circuit broken in two? How do you end up with two different levels of overcurrent protection on a single circuit?

I suspect that davidandkasie is closer to the real situation. Yeah, I know what I would run if the unit was not there- but it is! That is really ahead of the information typically available to the electrician. Now that the original poster is annoyed with me, I will say no more on this thread.

So, as the electrician on the job, what information would you have at rough in? I am imagining that you would run the furnace circuit and just leave it sticking out of the wall, then wouldn't you put in a junction box and run the armored cable to the furnace after it is installed? Or, does the HVAC tech usually do that? Wouldn't you at least have to know the requirements for the the furnace in order to size the branch circuit?

It clearly shows in the air handler manual a separate branch circuit listing for the heating element and for the blower/transformer (based on the particular heater installed). It shows the overcurrent protection, the minimum wire size, and the maximum wire length for each circuit. Am I misinterpreting this? Can this be done on a single circuit?

It is a Bryant...Anyone out there wired a Bryant split-system heat pump with electric heat back-up and integral shut-off switch? By wired I mean just removed the knock-out and connected the power?

Maybe I am just not explaining this very well...

the way mine is wired there ia a 100A feed to the airhandler from the main panel. this goes to teh lugs inside the airhandler. at that point, the factory wiring branches off to 2 breakers one for the heat strips and one for the fan. my old unit had 2 seperate sets of fuses for the same thing, and was fed by the same 100A circuit feeding the new AH.

if yours shows 2 different circuits coming to the AH, not broke out in the AH like mine, then you simply use a large enough conduit or flex to accomodate them. drill the hole out big enough to handle the proper sized connector.

Hi,
I'm assuming its a residential dwelling, and does the local authority having jurisdiction in your area require you to have the wire in conduit? If not you could easily run Romex or type NMC to the furnace. Its pretty common for Electrical furnaces to have 2 separate circuit feeder requirements. A great deal comes into play how far your furnace is from the panel board (Breaker box) as respects to voltage drop. Generally tho, Ac Furnace wires need to be rated at 125% and the overcurrent at 175%. Thus you need to look at the nameplate rating located on the furnace itself somewhere. Id really have to look at the furnace itself to make a proper judgement but to be safe id suggest you run a 4/2 (AWG 4-4-with ground for the 60Amp) and a 10/2 (AWG 10-10-with ground for the 20Amp) This method should have you covered.

jadriance,

My guess would be that your "dual-shutoff switch" *IS* two breakers, and you wire it up as its own subpanel.

Therefore, it creates your two branch circuits for you.

Just a guess. Don't quote me on it, but do review the documentation a time or two more and decide if this could be the case.

Jadriance,

We have wired set ups like this before, and some of them were Bryants requiring (2) circuits going to the interior furnace/air handler unit. The box on the furnace was not a sub-panel and it was not intended for only one circuit to be split inside of it. The reason for different circuits from the panel is that one circuit (the 20 amp you mention) is used for the controls only and the other (60 amp as mentioned) is simply a back up heater in case the heat pump cannot keep up with the heating demand.

To directly answer your question here is what I would recommend you do: Run your feeders from your main panel to a junction box on the wall, this way you can use NM cable to that point. Install flexible conduit from the wall junction to the furnace and route THHN feeders from the wall junction through the single flex conduit and into the furnace. Most of the units I have seen like this have a large enough knock-out to accomodate the required wiring.

The exact number of conductors and size of them would depend upon how far the run is from the main panel and the exact requirements from the manufacturer.

As a side note I am really not sure what all the fuss is about. This seems to be a pretty cut and dry issue to me.

This post is from 2 years ago.
I hope jadriance has figured it out by now.

Good catch. Someone brought it back to the top. I never look at the dates. :P