suggestions

[ModSquad]

Hey Guy's,

I'm at a loss here, just don't know waht to do. I'm pretty much done running my wires in the garage and this is what I have. 100 AMP subpanel

2 - 15 amp circuits for recepticals
1 - 15 amp circuit for the lights
1 - 15 amp circuit for the drop light, garage door opener and outdoor sensor light
1 - 20 amp circuit for recepts around the work area
1 - 40 amps going to the (attached Shed) which has lights a baseboard heater, some recepts and the compressor(5HP 1 stage 3 cyl pump FLA 21)
1 - 60 Amp for the welders/Plasma (I work alone so would never be using 2 or 3 at the same time)
1 - 30 Amp for the heater for in floor heat


Now as per many discussions on the electrical, I should be running 50 Amp breaker and min 8 gauge wire for the compressor. (21 x 175%= 36.75) (21 x 250%=52.5)

now the 8 gauge I alread had so was using it anyway no biggie, what my problem is the shed is attached to the garage, I will be using it to store parts and stuff in general as well as having the compressor in there (hence the baseboard heater to keep the room above freezing). The thing is, the shed has a subpanel of it's own(previous owner was running 40 Amps to it). so if I run leave it and run the 40 Amps to the shed subpanel from there would it be just too much to run the compressor off a 30 Amp breaker, the heater on 20 Amps and occasionally turn the lights on (4 - 4' bulb florescents 46 watts each)?

Or should I jsut say screw it and wire the compressor direct off the 8 gauge and a 50 Amp breaker, then buy some 10 gauge to run to the panel off a 30 Amp breaker? I'd have to purchase the 30 amp main breaker for the square D in the shed, and the 10 gauge wire, so I'm lookin around 120$. the other method, I have what I need.

Also, I'm going to have a PC with internet(for those quick search needs) and a TV with one of those cheap DVD's (20$ jobbies). before I put the drywall up, I'm thinking hard to put up 1 more 15 Amp circuit just for those, to leave my working circuits seperate. I could also theoretically use this last circuit for those hidden items that draw power(batterie chargers, possible bar fridge, etc..)

In my mind I know what I should do but having a hard time making that final decision, what do you think? and thanks

 

[trovato]

I don't know how to do this, or if it's even practical, but, here goes. You don't need the baseboard heater running while the compressor is running. The compressor will generate some heat, and if the heater just runs when the compressor is cycled off, I'm sure you won't get any freezing out there. Now, how do you make this happen? I'm not sure. Perhaps if there is a way to replace the compressor relay with a "double throw" one that powers the heater one way and the compressor the other. Of course, if this is all to save $120 it might be more trouble than it's worth.

 

[Charles (in GA)]

I don't know how to do this, or if it's even practical, but, here goes. You don't need the baseboard heater running while the compressor is running. The compressor will generate some heat, and if the heater just runs when the compressor is cycled off, I'm sure you won't get any freezing out there. Now, how do you make this happen? I'm not sure. Perhaps if there is a way to replace the compressor relay with a "double throw" one that powers the heater one way and the compressor the other. Of course, if this is all to save $120 it might be more trouble than it's worth.

The compressor, being in a remote shed will probably be left powered on all the time. This is not problem with good tight plumbing or a shutoff valve, I do it all the time, The heater, if like most I've ever seen has a thermostat, you set it and forget it. The whole idea is to keep the shed from freezing, so it will stay powered all the time in cold weather. I don't see how it is practical to switch from one to the other.

The real question is the actual rating of the heater. What is it wattage or amp draw of it, as found on the spec decal on it? A 1500 watt heater on 240v (not sure of voltage in Canada, or what the heater voltage is) is only 6.25 amps. I would set up the panel with the 8 gauge wire, use a 30 or better yet, a 40 amp breaker for the compressor and go for it. I'm willing to bet you won't have any problems.

Charles

 

[trovato]

The compressor, being in a remote shed will probably be left powered on all the time. This is not problem with good tight plumbing or a shutoff valve, I do it all the time, The heater, if like most I've ever seen has a thermostat, you set it and forget it. The whole idea is to keep the shed from freezing, so it will stay powered all the time in cold weather. I don't see how it is practical to switch from one to the other.

Charles

Right. What I was proposing was to turn them both into one logical item, a compressor/heater. That way, all of the above goals would be met, but without having them both drawing current at the same time. This is much like the way electric water heaters work, with two elements, but only one is energized at a time. Now, as far as this being practical, perhaps it is not.

 

[ModSquad]

yeah, that's what I was wondering.. the calculation is for a power spike. the FLA is what it draws for a cold start or if the motor binds. so I figured I'd be safe with 30 or 40. Worse case, it would trip. The heater is only 1500 Watt 240V, I just didn't know what the amperage that it draws was cause they are always installed on a 20 Amp Circuit. I just want to keep the shed a constant temp as the compressor is hard wired with a shut off box and will basically always be on. I don't want it to freeze (fairly new compressor).

If I'm running 40 Amps from the panel in the garage to a 40Amp main in the shed, can I run a 40 Amp breaker to the compressor? I know it won't draw that much, should I just make it a 30 Amp?

 

[Charles (in GA)]

yeah, that's what I was wondering.. the calculation is for a power spike. the FLA is what it draws for a cold start or if the motor binds. so I figured I'd be safe with 30 or 40. Worse case, it would trip. The heater is only 1500 Watt 240V, I just didn't know what the amperage that it draws was cause they are always installed on a 20 Amp Circuit. I just want to keep the shed a constant temp as the compressor is hard wired with a shut off box and will basically always be on. I don't want it to freeze (fairly new compressor).

If I'm running 40 Amps from the panel in the garage to a 40Amp main in the shed, can I run a 40 Amp breaker to the compressor? I know it won't draw that much, should I just make it a 30 Amp?

Since you are dealing with pure resistance heat, no motors or other things in which power factor becomes an issue, its simply a matter of 1500 watts divided by the 240 voltage equals the 6.25 amps.

Try a 30 amp and see if it works without a problem. If it doesn't (and its the same type or brand as your shop panel) simply use it in your shop panel for the 30 amp you need for the floor heater, and go out and buy a 40 amp to replace it.

Charles

 

[ModSquad]

cool, thanks for the advice Charles.. again, great resource!

 

[mpraddict]

What type of 8ga wire do you have? Not all types of 8ga are rated for 50 amps, especially aluminum. Not sure about Canada, just going from the NEC.
You're going to have to determine the startup load for the compressor and the load for the heater combined. Last thing you want is for the breaker to trip each time the compressor kicks on (and heat is on).

 

[ModSquad]

it's 8 gauge copper..
The FLA is full load amperage at 21 Amps, so I'm assuming that is the max amperage the motor will draw other then power spikes which is why they give you the 50 amp range right? the heater not sure, going by what charles was saying. but basically, it's a regular old baseboard heater that was installled in this house abou 30 yrs ago. it's being replaced and I figured I'd just throw it in the shed.

 

[mpraddict]

8ga copper should be ok but not over 50Amp. FLA (full load amp.) is the max the motor is rated for during normal operation IIRC. There is always a spike when the motor starts up, LRA (locked rotor amp.) and that's why the manufacturer will specify the breaker size, seemingly too large for the current draw.
Does this help?

 

[ModSquad]

ah, yes.. I misunderstood the terms.. thanks. I'll look at the LRA, I believe it's also listed on the plate. I think I'll be ok tho. I'll post up what it is.. it wouldn't be over 50 amp for sure.. I'm currently running 40 amps there. but it was just installed temp to get lights and current heater running(construction heater).. I'm hopeing to finish the rest of the wiring and have the insulation complete by EOW this week..