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-   -   Sub Panels (http://www.diychatroom.com/f18/sub-panels-20823/)

BillyD 05-09-2008 04:13 PM

Sub Panels
 
What would be the best way to add sub panels rather than just one distribution panel. How would you feed them to Basement and garage. Add breakers in the main box or have distribution buss to connect to?
This is not new construction.
Thanks

Termite 05-09-2008 04:32 PM

This is a very general question, and we need specifics.

A sub panel is fed off of the main panel using a double breaker that catches both the A and B phases. The feeder wires are sized based on the size of the breaker in the main panel that serves the sub panel.

In a sub panel, the circuits' neutrals must float...Or be isolated from the grounds. The neutral bar must not be bonded to the panel jacket. This is incredibly important.

When putting a panel in the garage, you must not recess it in the sheetrock due to the fact that the sheetrock in your garage is a fire membrane that cannot be penetrated by electric boxes larger than 16 square inches. Most folks face mount them on the wall, and a wall can be furred out around them to give a recessed appearance but leave the fire membrane intact.

As far as getting the wire to the garage...Totally depends on the house.

This isn't DIY stuff for most people, so unless you're a competent electrician, which by the nature of the question I'm assuming you're not, I'd strongly suggest hiring this out.

BillyD 05-09-2008 05:00 PM

I follow everything you say except what is a floating neutral and why not bond it to the panel jacket?
Thanks
Billy

Termite 05-09-2008 05:25 PM

Quote:

Originally Posted by BillyD (Post 122096)
I follow everything you say except what is a floating neutral and why not bond it to the panel jacket?
Thanks
Billy

Bonding only occurs at the point of service. It MUST NOT occur at the sub panel. You have a neutral bar on each side of the breakers. Use it for neutrals and remove the green bonding screw to break its continuity with the panel jacket. Land all your neutrals in this bar(s). Then add a dedicated grounding bar to the panel jacket and land all of your grounds there. I can't stress the importance of doing this correctly enough to you.

No need for waterline ground/driven rods off a sub panel.

Once again, let me stress that you need an electrician to assist you.

mr500 05-09-2008 05:49 PM

Yes, again the grounds and neutrals must land on a separate ground buss. In MY situation, I just went out and bought the equipment ground buss that fit my box. Then landed all my grounds to that.

Since this panel(s) will be in the house, you don't have to add more gnd electrodes. I had to pound in an 8 foot one and it was SOOO fun!!

Decide also how much power you will need to run. Thats critical in the buying wire and panel stages. Very critical!! You cant take wire back after it has Benn custom cut at most places

BillyD 05-09-2008 07:30 PM

I respect all you are saying but no one has explained why it must be an isolated ground or what is a floating neutral. Please help us newbies understand.
Thanks for your help.

mr500 05-09-2008 08:05 PM

Quote:

Originally Posted by BillyD (Post 122134)
I respect all you are saying but no one has explained why it must be an isolated ground or what is a floating neutral. Please help us newbies understand.
Thanks for your help.

This might help. read this thread..post #9 from stubbie


http://www.diychatroom.com/showthrea...775#post121775

BillyD 05-11-2008 06:56 AM

I read the posting and it is very well written. The subject of a floating neutral never came up. What is hard to understand is wouldn't you want the same set up and protections in a sub panel as you would the main panel? Someone please explain why it is incredibly important to have a floating ground.
Thanks

chris75 05-11-2008 09:24 AM

Quote:

Originally Posted by BillyD (Post 122456)
I read the posting and it is very well written. The subject of a floating neutral never came up. What is hard to understand is wouldn't you want the same set up and protections in a sub panel as you would the main panel? Someone please explain why it is incredibly important to have a floating ground.
Thanks


For one it would be a violation, also it is so that dangerous (neutral) current will not flow on the metal parts of the electrical systems.

An improper neutral-to-ground connection can create a condition where neutral current has multiple parallel paths to return to the power supply,
Objectionable (neutral) current flowing on the metal parts of the electrical system can cause fires, electrocution, and power quality issues with sensitive electronic equipment.

jwhite 05-11-2008 09:26 AM

Maybe I can help. Draw a simple circuit with a hot going to a light then back to the panel. Next draw a seperate line (the ground) from the panel the the metal housing of the light fixture.

Imagine what would happen if the ground and neutral were tied together at the light fixture and the neutral were to become open. All of the current that should have been traveling back on the neutral is now traveling back on the ground, which is tied to the exposed metal parts of equipment. Someone touching these metal parts could be killed.

So the real question is then Why do we bond the ground to the neutral at all? The reason is that if we did not, a hot to ground fault would not trip a circuit breaker.

Since we need to have a neutral to ground bond, we do it at the safest place in the system as possible. The main panel.

Since feeder drops from the utility to the home are three wire without a ground, if the neutral were to open between the main panel and the utility transformer, everything in the house would stop working, so the hazzard is likely to be fixed right away.


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