I have a 150 Amp service connected to a main breaker panel which has less breaker space than I need.
Is it OK to add a 100 amp breaker to the existing panel and sub-feed down to another panel with more spaces.?
The load for the building will not exceed 150 Amps.
The Moving Finger writes; and, having writ,
Moves on: nor all your Piety nor Wit
Shall lure it back to cancel half a Line,
Nor all your Tears wash out a Word of it.” – Rubaiyat of Omar Khayyam
Moves on: nor all your Piety nor Wit
Shall lure it back to cancel half a Line,
Nor all your Tears wash out a Word of it.” – Rubaiyat of Omar Khayyam
Replies
yes
Like he said, yes. But, a subpanel is not wired exactly the same. In addition to hot(s) and ground you need to carry a neutral, too, and in the subpanel box the neutral and ground buss bars must be electrically disconnected from one another. Most panels have a screw or strap that can be removed to perform the conversion. Ask at the counter of the electrical supply house.
The existing box has only three wires for the service, two hots and a ground.
All the white wires and the bond wires are connected to the same ground terminal strip. I guess thats what was required at that time.
If theres a way to separate them I don't see it.
The box I am adding has a strap connecting two grounding terminal strips. I can remove this strap and separate the bond wires from the white wires but I don't see the point when all the bonds and grounds are connected together in the existing box.
If I separate the bonds and grounds in the sub feed panel and run a separate green wire up to the existing panel seems like that would be same as not removing the strap.
The Moving Finger writes; and, having writ,Moves on: nor all your Piety nor WitShall lure it back to cancel half a Line,Nor all your Tears wash out a Word of it." - Rubaiyat of Omar Khayyam
In the main panel the neutral and grounds are connected together -- they share the same buss bar, or both buss bars are grounded to the box. By code, in a subpanel, they must be separate.
I fear being unclear or misunderstood by explaining it in writing. Have the electricians manning the counter at the supply house demonstrate for the particular panel you bought how to properly separate the buss bars. Every panel design is slightly different. They will also explain what type and size wire to use for the connection.
arrow, you might not see the point but that's the way it's done if you want to do it right.
In a subpanel the grounds and neutrals are kept separate. Period. There are reasons but someone else can get into the explanation if they want.
The busbar for the grounds wants to be bonded to the sheetmetal of the panel. The busbar for the neutrals wants to be isolated from the sheetmetal of the panel.
Ed
Edited 6/30/2007 10:26 pm ET by edlee
arrow, you might not see the point but that's the way it's done if you want to do it right.
Yep, bad things can happen if you tie the neutrals and grounds together at a subpanel: sparking furnace ducting, shocks from plumbing fixtures, etc. It's hard to explain why in words, but it's against code and just don't do it.
The existing box has only three wires for the service, two hots and a ground
There in lies the problem,.... proper nomenclature.
Your existing main panel has two hots and a neutral wire from your service entry drop through the meter base.
The difference between a neutral and a ground wire is important. A neutral is defined as a current carrying conductor in a normal circuit. A ground, or what you are calling a bonding wire, is not a normal current carrying conductor. It is another path to earth ground for fault currents to follow.
The reason you do not electrically connect the ground and neutral bus in a sub panel is straight forward. You do not want a fault in any of the sub panel circuits to go back through your main panel. You want them to go to a closer earth ground.
Repeat this mantra,...... a ground is not a neutral, a ground is not a neutral, a......
Dave
You sound just like Cliff Popejoy in an article a few years back in the mag! Right on
Have a good day
Cliffy
"The difference between a neutral and a ground wire is important. A neutral is defined as a current carrying conductor in a normal circuit. A ground, or what you are calling a bonding wire, is not a normal current carrying conductor. It is another path to earth ground for fault currents to follow.The reason you do not electrically connect the ground and neutral bus in a sub panel is straight forward. You do not want a fault in any of the sub panel circuits to go back through your main panel. You want them to go to a closer earth ground."Not exactly.Normally I used "ground" like most people, but the term has several meanings.There are 2 "ground".The ground electrode system. That consists of ground rods, metallic underground water pipes and similar electrodes along with the grounding electrode conductor. It is bonded to the service entrance and the service neutral. It's purpose is to reference the electrical system to the earth and also to handle surges outside the home.The other ground is the EGC (equipment grounding conductor). I serves 2 purpses. One is to handle fault currents INSIDE THE HOUSE. If there is fault from the hot to the case of an appliance the EGC connected to the case will divert that current back to the panel where it is bonded to the neutral. And you want that current to go back to the main panel. That is the only place that EGC is bonded to the neutral.If, instead, the current went back to ground electrodes they can have a relatively high resistance and allow dangerous voltages on the applice.If it is a small leakage current the case will stay at zero and be safe. If it is a dead short then the circuit breaker will trip. The other purpose of the EGC system is to insure that any metal parts in a home that you can come into contact with is at the same potential, with in that building.The only way tht you can guarantee it is to use a common circuit (the EGC) that is designed to not carry any current in normal opperation.Gas pipes and furances are bonded (often through the EGC) along with metialic water lines (if not already a ground electrode) to the neutral/ground electrode system at the service, but only at one point.If the neutral and EGC are also connected in a sub-panel then you will have some current flowing in that section of the EGC and thus it won't be at the same potential as other parts of of the EGC system.And if you have failr of the wire or connections between the sub-panel and the main the cases of all of the equipment of that connects to the EGC can become hot..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
> The load for the building will not exceed 150 Amps.
The load for the building should not exceed 80% of the main breaker capacity.