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What is minimum size ground do I need for a 200 amp panel? I need to bond the hot and cold in the water heater and already have a ground rod in the ground. I also need to bond the water and gas.

marked as duplicate by Steven, wallyk, Doresoom, Niall C. Jul 22 '15 at 13:49

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  • What is the biggest wire you have in the house? – Tyler Durden Jul 21 '15 at 14:30
  • Is this a single family home, or multi-family home? – Tester101 Jul 21 '15 at 14:52
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    I vote to reopen this question. In my opinion, it is not a duplicate of the other question. – Tester101 Jul 24 '15 at 18:47
  • Decided to leave this question closed, since it was originally closed by 4 of our more active users, and also because the OP didn't seem to care either way (didn't comment or raise reopen flag). – Tester101 Jul 31 '15 at 11:41
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According to National Electrical Code, the water piping must be bonded to the service equipment enclosure, the grounded conductor at the service (service "neutral"), the grounding electrode conductor (where large enough), or directly to one or more of the grounding electrodes. The bonding jumper is to be sized using Table 250.66. For 200 ampere service, you'll probably be using 4 AWG copper or 2 AWG aluminum.

For gas piping, you can bond it to the same things as mentioned for water piping. However, the sizing of the jumper comes from Table 250.122, and is based on the size of the circuit that is likely to energize the piping.

For example:

If you had a gas furnace that was fed by a 15 ampere circuit, the jumper could be 14 AWG copper or 12 AWG aluminum. Since the furnace circuit is the most likely to energize the piping, you'll size the jumper based on the ungrounded conductor feeding that circuit. This is a somewhat controversial topic, as some believe the jumper should be larger.

National Electrical Code 2014

Chapter 2 Wiring and Protection

Article 250 Grounding and Bonding

250.104 Bonding of Piping Systems and Exposed Structural Steel.

A) Metal Water Piping. The metal water piping system shall be bonded as required in (A)(1), (A)(2), or (A)(3) of this section. The bonding jumper(s) shall be installed in accordance with 250.64(A), (B), and (E). The points of attachment of the bonding jumper(s) shall be accessible.

(1) General. Metal water piping system(s) installed in or attached to a building or structure shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or to the one or more grounding electrodes used. The bonding jumper(s) shall be sized in accordance with Table 250.66 except as permitted in 250.104(A)(2) and (A)(3).

(B) Other Metal Piping. Where installed in or attached to a building or structure, a metal piping system(s), including gas piping, that is likely to become energized shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or the one or more grounding electrodes used. The bonding jumper(s) shall be sized in accordance with 250.122, using the rating of the circuit that is likely to energize the piping system(s). The equipment grounding conductor for the circuit that is likely to energize the piping shall be permitted to serve as the bonding means. The points of attachment of the bonding jumper(s) shall be accessible.

NOTES:
- If this is a multifamily dwelling, the sizing might be a bit different.

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Having a big ground does not matter if all the other wires are tiny because they will melt before the ground does. As long as the ground is bigger than any of the wires in the house, then it is sufficient. Usually the biggest wire is the one going to the oven or a dryer. The amperage rating of the box does not matter at all. For example, the box is 500 amps and the biggest wire is 100 amps. Then having a 500 amp rated ground is pointless because the 100 amp wire will melt long before the ground will.

The best ground is an 8-foot copper rod you drive into the ground with a sledge hammer. Then you clamp a braided copper grounding strap to it. Good idea to put it in PVC tubing to protect it from rain. For a house, the strap typically is 1/2" wide or larger.

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    In an overcurrent situation, the ground has nothing to do with the other wires melting. Many houses do not have a grounding rod since the ground and neutral (from the utility) are tied together at the main panel. The ops question is about gauge of wire required for the ground and your answer does not address this. – Steven Jul 21 '15 at 15:02
  • Yes it does. The wire should be as big as the biggest wire in the house. – Tyler Durden Jul 21 '15 at 15:04
  • If there is an overcurrent then there is not a ground fault and no current will flow on the ground wire. You can reference the tables in this answer diy.stackexchange.com/questions/15280/… where the ground wire size is dictated by the size of the service entrance conductors, not the largest conductor beyond the service entrance. – Steven Jul 21 '15 at 15:07
  • @Steven That makes no sense. If 100 amps are flowing to, say the oven, and it shorts out to the frame of the oven then goes to ground, the ground wire must be able to handle exactly the same current going INTO the oven which is 100 amps. If the ground wire can only handle, say 20 amps, then it may melt and disconnect. In that case what happens is that the current stops flowing and the housing of the oven becomes electrified possibly killing whoever touches it. – Tyler Durden Jul 21 '15 at 15:24
  • No. The required ground wire size is probably #6 AWG (see here) even though power is supplied by 4/0. The purpose of the ground is not to reroute full power delivery to ground, but to eliminate the potential between ground and incorrectly energized appliance casings, etc. No appliance is on a branch circuit so heavy that a modest size ground can't trip the breaker in the case of an electrical fault appearing. – wallyk Jul 21 '15 at 15:31

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