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floydl13

02:00PM | 09/28/06
Member Since: 09/27/06
4 lifetime posts
Bvelectrical
I have a sub panel in my garage & would like to update the panel with a new one that has breakers. I inspected the wires from the main panel, there are two #8 hot wires coming to the existing sub panel. My question's are:

Can I install two 20amp breakers on one line & a 30 amp breaker on the second.

I'm assuming I can put up to 40amp's on each circuit since they are #8 wires, is this correct.

Thanks,

Floyd

Floyd

Billhart

04:26PM | 09/28/06
Member Since: 04/25/05
1915 lifetime posts
#8 COPPER wire is rated for 40amps if the insulation and terminal connections are rated for 60*C.

However, if this is newer wire with 75*C ratines (or better) and the feeder breaker and sub-panel are rated for 75* C then it can be used at 50 amps.

What is the size of the feeder breaker?

Is this garage attached or detached?

"I have a sub panel in my garage & would like to update the panel with a new one that has breakers."

I am guessing that the existing uses fuses. If that is the case them the feeder wires might also need to be replaced to bring in a ground wire.

The size of the sub-panel and the feeders are based on what the loads will be. Not the total of breakers that will be used.

What loads to you want to power off the panel.

"Can I install two 20amp breakers on one line & a 30 amp breaker on the second."

A 30 amp 120volt load is very unusual. What is this for.


floydl13

07:29AM | 09/29/06
Member Since: 09/27/06
4 lifetime posts
Hi,

Thanks for getting back so quickly.

I looked at the feed breaker on the main panel & they are both 40 amp. They are both pig-tailed together. I assume this was because of the electric dryer that was once located in the garage. The 220 oulet has been removed, so I believe I can remove the the pig-tail accross the breakers.

My garage is detached from the home and I would guess the line to be about 50 feet. (Main panel from sub panel)

Thanks, Floyd

Floyd

floydl13

07:56AM | 09/29/06
Member Since: 09/27/06
4 lifetime posts
Yes the existing does use fuses. Could I just add a ground rod to the sub panel. there is a white #8 wire already coming into the Sub from the main. Which is the ground back to the main for both circuits.

My load fo the 30 amp breaker would be for a compressor & I would like to buy a welder that operates on 110v.

The rest of the loads are:

Lights

Washer

Gas Dryer

Frig

TV & Cable Box

Outlets for work Bench.

Floyd

Billhart

02:58PM | 09/29/06
Member Since: 04/25/05
1915 lifetime posts
That white wire is the neutral.

However, with a sub-panel in a building or a detached building with METALIC connections between the building requires a separate NEUTRAL and GROUND conductor.

And with the water, gas, and phone/cable you have metallic paths.

You need to upgrade the wiring.

And isolate the neutral bus in the sub-panel. Depending on the panel you might need to also get an addon ground bus kit.

And you need to install a ground rod at the outbuilding and connect it to the ground bus.

Now, as to the size requirements. It would problem work with 40 amp, but since you need to upgrade the wiring anyway using modern wire you can go to the 50 amp colum.

But you really need to know rating on the appliacnes and equipment.

Specially the welder and compressor.

But figure 20 amps for the work bench receptacles.


floydl13

03:35PM | 09/29/06
Member Since: 09/27/06
4 lifetime posts
Ok Bill, I'm Confused. I have a existing sub panel with screw in fuses. I don't understand why I need to change the three #8 wires coming in from the main panel. All I was trying to do was put in a new sub panel to upgrade the old one. If I have two hot & 1 neutral wire coming from the main panel, why can't I use those & add a grounding rod to the outside of my garage & attach it to the new sub-panel. I was going to upgrade all the wire's & circuits in the garage to have a seperate ground wire.

Oh I almost forgot, doesn't the metal conduit between the main panel & sub panel act as a ground between the two as well. If not couldn't I just add one ground wire to that run, instead of replace all the wire's.

Thanks,

Floyd

Billhart

08:13PM | 09/29/06
Member Since: 04/25/05
1915 lifetime posts
"Oh I almost forgot, doesn't the metal conduit between the main panel & sub panel act as a ground between the two as well. If not couldn't I just add one ground wire to that run, instead of replace all the wire's."

Yes, that makes a big difference.

If the conduit is metal and continous from the sub-panel to the main panel then it can be used as the ground conductor.

The remainder of my comments about isolating the neutral bus and the ground rod apply.

Too often the conduit is only used to protect a CABLE until it goes under ground or PVC conduit is used.

Don't have time to for detailed explanations, but it is important that every thing "grounded" that you might come into condtact with be the same potential. That include the water pipes, tv cable, etc and the electrical grounded equipment. The only way to insure that is to have a EGC (equipment grounding conductor; aka THE GROUND) that is never carries any current. It is tied to the neutral at the sub-panel then it will be carrying current and thus a potential difference.

With the isolated neutral then all of the grounds are refereced to a single point, the main panel where the EGC, ground electrode system, and neutral are bonded together.

A ground rod at the sub-panel can not be used withou the EGC as it can't sink enough fault current to trip a breaker. It's purpose is for voltage surges that might come from the outside via lightning strikes.


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