Please Help Me Cover My ***... Another Sub Panel Wiring Question

[StumpFJ40]

It's been a while since I posted here due to a string of events that diverted focus from my hobbies to the real world (military retirement, job hunting, job finding and moving).

Now that I've landed, I am building my shop back up in the attached 2 car garage and need to wire up my Hobart 210 welder and CH 60gal compressor.

Situation: There is an HVAC unit in a closet in the attached garage which is fed thru a disconnect (also in the closet) by a 4AWG Cu THHN SE (2 conductors and ground) cable from a 60A breaker in the Square D QO main panel .

Plan: Replace 60A breaker in the main panel with a QO 90A breaker and replace the disconnect with a sub panel in the closet to hold 220v breakers for the welder (30A), compressor (20A breaker (15A draw stated on motor sticker)) and HVAC (60A max over current device required as per the information sticker on the unit). I will use 10AWG wire for the compressor and welder circuits. I know 10ga is overkill for the compressor, but it is a short run and I have 100 ft of it.

Questions: 1. My understanding is that since the sub panel is exclusively feeding 220V loads, it is within code to use 2 conductor cable (separate neutral and ground not required) to supply the sub panel, am I correct?
2. Am I within code to install a 90A breaker in the main panel and supply the sub panel through 4AWG Cu wire since the stated ampacity of the cable is 85A and I can up amp the breaker?
3. Is 90A sufficient to supply power to the combination of the HVAC, compressor and welder, or am I at risk of overloading the feeder and tripping the 90A breaker in the main panel?

Thank you in advance for your advice.

Cheers,
Stump

 

[StumpFJ40]

Sooo, since silence is tacit approval I'm off to the store to buy the objects of destruction.

 

[Norcal]

By the size of the feed to the HVAC equipment I am taking guess that it is heat pump, it's not a good idea to take over a dedicated feeder & add to it.

 

[StumpFJ40]

The cable does, indeed, feed the heat pump. That was my initial concern until I saw the size of the feeder. My thought was that since the feeder is 4awg, it could handle the combined load of the HP @ max 60A and either the comp or the welder, in in the event the HP came on when using one of them.
Is this a false assumption?

 

[Norcal]

What is the back up heat? Gas or electric?

 

[Norcal]

Code wise you would be better off with a new feed to your panel.

 

[wyliesdiesels]

What is the HP rating of the compressor?

 

[Charles (in GA)]

Sub panel needs a four wire feed. The fact that you are running only 240v loads from it means nothing, the panel is CAPABLE of handling 120v loads and you may very well in the future do so, or someone after you will. Without a neutral, everyone is screwed.

 

[StumpFJ40]

Compressor is an older "5HP" rated motor the motor states 15A, but I know they have a higher startup load and that may stress the feeder if the HP is running when it kicks on.
The backup (auxiliary) heat is electric as well. There are 30A and 60A feeds to the heat pump unit. I assume the 30A is for the fan, but I am largely ignorant to the black magic of the heat pump.

 

[StumpFJ40]

Sub panel needs a four wire feed. The fact that you are running only 240v loads from it means nothing, the panel is CAPABLE of handling 120v loads and you may very well in the future do so, or someone after you will. Without a neutral, everyone is screwed.

I have not seen code that dictates 4 wire for a dedicated 220 sub panel, though I can only say that I've seen the 3 wire sub panel online here: http://waterheatertimer.org/images/Inside-Main-Subpanel-240Volt-300.jpg

 

[Zeke]

I have not seen code that dictates 4 wire for a dedicated 220 sub panel, though I can only say that I've seen the 3 wire sub panel online here: http://waterheatertimer.org/images/Inside-Main-Subpanel-240Volt-300.jpg

You must be reading code books from 20 years ago. You can however use a bonded conduit as the equipment ground.

 

[StumpFJ40]

If the circuits are all 220V then there is no neutral, just two 120v legs and a ground correct? If the feeder ground is grounded at the main and the circuits are grounded at the sub panel and the box grounded, isn't that the same as bonded conduit?

 

[wyliesdiesels]

Compressor is an older "5HP" rated motor the motor states 15A, but I know they have a higher startup load and that may stress the feeder if the HP is running when it kicks on.
The backup (auxiliary) heat is electric as well. There are 30A and 60A feeds to the heat pump unit. I assume the 30A is for the fan, but I am largely ignorant to the black magic of the heat pump.

Theres no guessing about it.

U would need to do a load calc to figure out if the feeder can handle the additional load.

Personally i wouldnt want the headache of the possibility of loosing my heater and having to go reset the breaker because i was too cheap to run a separate subpanel.

 

[StumpFJ40]

I appreciate the feedback.

Load Calculation:

Feed: 21600VA

HP: 9600VA (per spec sheet on unit)
Welder: 6000VA
Comp: 3600VA
Total: 19200VA

Based on load calc, the 90A feed will support the loads.

This is not a permanent solution, just a measure to get my shop going. I will run a dedicated feed as soon as practicable.

 

[Norcal]

If the circuits are all 220V then there is no neutral, just two 120v legs and a ground correct? If the feeder ground is grounded at the main and the circuits are grounded at the sub panel and the box grounded, isn't that the same as bonded conduit?

May be splitting hairs but 220V has a line and a neutral & is 50 Hertz, standard voltage in the US is 240V.

I am not keen on taking a dedicated circuit & turning it into a subpanel feed. Pictures would be helpful.

 

[StumpFJ40]

Yeah, I used 240 for the calcs. Pics are coming.

 

[nsula_country]

Compressor is an older "5HP" rated motor the motor states 15A, but I know they have a higher startup load and that may stress the feeder if the HP is running when it kicks on.
The backup (auxiliary) heat is electric as well. There are 30A and 60A feeds to the heat pump unit. I assume the 30A is for the fan, but I am largely ignorant to the black magic of the heat pump.

The 30A and 60A feeding the air handler are for resistive heat. This is your electric "emergency heat" and also what keeps you warm while the heat pump is in "Defrost Mode," which happens more frequently the cooler the weather gets.

Unless, it was wired to not engage electric heat on defrost. Some do this for energy savings. I tried this method when I installed our heat pumps in 2011, wife did not like the effects. Ours kick in electric heat during defrost mode.

There is no neutral on this circuit. The fan is 240v, ran off one of the two circuits. Both have to be on the operate (most brands).

I would just pull a new feed, 4 wire, and sub panel. Life will be better this way.

CT

 

[StumpFJ40]

I understand using the HP feed is not ideal.
I just thought that since they went overkill on the feed that I could use the extra ampacity of the wire to supply power to some other infrequently used items. All the 120v is supplied by the main since this is an attached garage.

Since this is temporary, do you see anything hazardous about this setup, or is it only a potential nuisance from a tripped breaker?

 

[nsula_country]

I understand using the HP feed is not ideal.
I just thought that since they went overkill on the feed that I could use the extra ampacity of the wire to supply power to some other infrequently used items. All the 120v is supplied by the main since this is an attached garage.

Since this is temporary, do you see anything hazardous about this setup, or is it only a potential nuisance from a tripped breaker?

It's not over kill. Electric heat on that unit needs 70+ amps.

If you really want to use it for 240V utility use, you can. But I'd leave the 60 amp breaker in place. Also, you will need to turn off the HP each time you use air or weld. It will trip if both run.

CT

 

[StumpFJ40]

I'm confused, if it has a 60A breaker feeding it, how could it require 70A? The HP is a smaller unit for about 1200sf of space. I'll have to check the size, but at less than 10000kva it isn't big, right?
I accept that I may have to secure the HP when running these other loads, but that will be the extra motivation to install the dedicated line.
Thanks again for the input, I am learning.

 

[nsula_country]

I'm confused, if it has a 60A breaker feeding it, how could it require 70A? The HP is a smaller unit for about 1200sf of space. I'll have to check the size, but at less than 10000kva it isn't big, right?
I accept that I may have to secure the HP when running these other loads, but that will be the extra motivation to install the dedicated line.
Thanks again for the input, I am learning.

Unless it is a very small heat strip, they normally have two feeds. 60A is common for circuit #1, 30A-60A is normal range for circuit #2.

Are you sure there is only one feed? Most have two. 10kw will run off a single 60. Anything larger will require two circuits. You stated there was a 30A and a 60A breaker feeding the AH (air handler). When I said 70+A, I was speaking of the heat strips in total, not the circuit feeding PART of the heat strips. I assume now that you are only wanting to use the 60A feed, that happens to have 4ga wire and leaving the 30A alone (probably 10ga.)

IF you are set on using the 60A circuit i would suggest finding a manual for your specific AH and ensuring the HP defrost cycle is not tied to the heat strip controls. All will work fine, but will just not have as fast of temp rise... HP's are MUCH more cost effective than resistive heat anyway.

As for bumping the breaker to 90A because the wire is 4ga. Is this really necessary?

Will you be welding at max current when the compressor starts and the HP is in defrost mode?

Will you use the 90A to feed a sub-panel and continue to feed the AH with the 60A per its design?

If not, will you forget to put the 60A back in place if/when you run a dedicated sub-panel to the welder and compressor? The 60A is not just protecting the wire here, it's protecting the heat strip. Hence RECOMMENDED breaker size dependent of kw rating of heat strip.

I'm not trying to get in your stuff, it's your house. But you asked for advice and we feel it's not a good idea. I would not be taking the time to type this if I wasn't knowledgeable in the fields of Electricity and HVAC...

Will it work, of course. But may have mixed results depending on your level of success expected.

CT

 

[StumpFJ40]

You are not getting in my stuff at all. I absolutely appreciate the knowledge! I will look into the issues you brought up. It does have 2 inputs, a 60A and 30A feed. I was totally unaware of the defrost mode.

 

[StumpFJ40]

I regularly prove the adage of "you learn something new everyday".

I could not find any data on the defrost mode for my system.

I will probably not be welding at max current when the AH comes on.

The 90A would come into the breaker box and I would have a 60A, a 20A and a 30A breaker for each piece of equipment.

I dont think I would forget about the 90A breaker since I would locate the dedicated sub panel elsewhere and would be returning the AH 60A feed to a simple disconnect.

 

[greenlizard]

For more background info: I recently installed a sub-panel in my attached garage. After much reading I used 3 awg copper for the two hots and the neutral and a 4 awg copper for the ground. That's four wires, all in two inch conduit. This is powered by a 90 amp breaker in the main house panel.
In the sub-panel I have 4 20 amp 120 volt general use circuits, 1 60 amp welder circuit, and 1 20 amp 240 volt circuit for my compressor. I ran 8 awg for the welder, and 10 gauge for the compressor.
The 90 amp service is more than I'll ever need but pulling that heavy wire is such a pain I only wanted to do it once.
Good luck with your upgrade.

 

[CNGsaves]

Why not just skip over the "temporary" step and go right to . . .
. . . . Do It Right The First Time !!!

You'll never regret having plenty of power in garage with appropriate subpanel.

GJ Sparky's will give you all the details you need, and cheapest way to do it.