I am helping a friend wire his new (owner-built) house. He was advised that he would have to have a disconnect installed between the meter and main panel, even though the distance between them is only 2 feet. He was also advised thath he would need 4-cable service wire, 2 hots with separate neutral and ground wires.
Has the requirements changed in the past few years? All I an familiar with is 3-wire service entrance cable, 2 hots + neutral. And I didn’t think you would need a disconnect with only 2 feet between the meter base and main panel.
Would appreciate any advice.
vlperk
Replies
This is usually a local jurisdiction decision, but most now require an outside disconnect even if the service entrance and panel are back to back. Once you wire in a disconnect, every panel on the load side is considered a subpanel and must be wired accordingly (2 hot, 1 neutral, 1 ground, ground and neutral buses separated).
Let me make sure I understand correctly. Three wires into the meter base. Four wires from the meter base to the disconnect. And then four wires from the disconnect to the main panel.
Or is it four wires just from the disconnect to the main panel; and three wires everywhere else?
And the disconnect must always be outside; not inside?
Thanks again for your help.
Edited 11/11/2003 6:56:50 PM ET by vlperk
its four wire everywhere, just think of them as pos,pos,netural and ground.
In some places, like where I live, the meter base serves as the disconnect. In case of a fire, they just pull the meter. But, while this does disconnect the power it also leaves the hot lugs exposed unless they put a cap over it. The firemen are not always happy to fool around with meter boxes, so some places require a separate disconnect. Its often outside since the main breaker in the panel serves the same purpose if you're inside the house. But, I think placement of the disconnect is decided locally. Check with your building department.
Thanks everyone for the information. However, as sometimes happens on this forum, you get somwhat conflicting advice :-)
I will check with the AHJ and power company; however, would like to know your advice regarding proper wiring of the service entrance if I do, in fact, use a separate disconnect between the meter base and the main panel.
It makes sense to me that I would ground the system at the disconnect, and use an unbonded ground (isolated neutral) in the main panel. If that is the case, then to me at least, it would appear that I would need a 4-wire connection only between the disconnect and the main panel; and would have 3-wire cable feeding the disconnect. Is this correct? If not, and 4-wire cable is required to feed the disconnect, are meter bases readily available with 4 terminals on the outfeed side, and are disconnects available with 4 terminals on the infeed side?
Thanks again for all your help,
vlperk
In my area (NW Ohio) you would run 3 cables from the meter to the main disconnect, 2 hots and a neutral.
From the main disconnect you would run 4 wires to the main distribution panel (which is a sub-panel becasue of the separate disconnect):
2 hots, a neutral, and a ground. The neutral and ground would be connected in the main disconnect box.
In the main panel, you would remove the bond bar/connection between the neutral and ground bars, and you would put all circuit neutrals on one bar and all circuit grounds on the other.
The neutral bar shoud also be electrically unconnected from the main panel housing; the ground bar should be conected to it.
You would also run a grounding electrode from the main disconnect to appropriate grounds - water main, driven rods, rebar, whatever is appropriate in your jurisdiction.
_______________________
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Your mileage may vary ....
The usual thing here is for the meter base and disconnect to come from the factory as a single one box unit. The disconnect is just a big breaker (or two if it's a 400 amp service). It's the official "service entrance" where ground and neutral get connected.
From the weatherhead to the box it's three wires. The line from the ground rod and plumbing enters the picture here. From there on out, it's four wires.
-- J.S.
Thanks again everyone. Just finished the job, and yes, the disconnect was integral with the meter base. (Also, it was obvious which was the ground wire after I removed the outside covering from the 4-wire cable :-)
Thanks again,
vlperk
The disconnect is outside so the firefighting persons can get to it.
3 wires from utility to meter.
3 wires from meter to disconnect.
1 wire from earth ground to disconnect neutral/ground connection.
4 wires from disconnect. Neutral/ground connection to distribution/breaker panel neutral buss and Neutral/ground connection to distribution/breaker panel ground buss.
Ground busses/wires and neutral busses/wires to be isolated from each other everywhere except the connection at the disconnect.
SamT (used to be a 'tronics tech)
I recently had to disconnect the service from a house twice, four weeks apart, and would have loved a disconnect meter base. The utility said it would be fine for me to have one installed by my electrician if I wanted to spend the money. Otherwise, there is the meter at the property line and the underground cable to the house is energized unless you pull the meter. We had house movers raise the house and for everyone's sake it's prudent to de-energize the underground cable and disconnect it physically from the main panel. To do this we needed the utility out four times--pull the meter, put it back, pull the meter, put it back. That was a major hassle, but fortunately no utility charge. I realize your scenario is different with the meter and the main service close together, but I will go for a disconnect on the meter base next time. I'm also a volunteer firefighter and we definitely like easy access to shutoffs for power and gas, preferably stuff we can find easily in the dark and that isn't stuck open.
Thanks everyone, this has been a very helpful discussion. As they say, praise the day you learn something new!
vlperk
Oops, one more question: When using the 4-wire cable from the disconnect to the main panel, which gets the smaller wire, the neutral or the ground? The SE wire we are using is 4/0, 4/0, 4/0, 2/0. Not sure if the smaller (2/0) wire is for the neutral or the ground.
Thanks again,
vlperk
the ground is one size smaller. also the meter box get grounded to the ground rod too. so its really four wires not three. just go buy the book at HD it explains everything simply. Tauton "wiring a house"
The best employee you can have but you wouldn't want him as a neighbor " He the shifty type"
Edited 11/13/2003 9:20:21 PM ET by BROWNBAGG
The disconnect switch must be the requirement of your particular electric utility, not all require it. Each utility has their own particular rules that don't necessarily agree with others. Check with them first, they should be able to provide you with the proper information and probably a sample diagram showing just how to wire things and where to locate them. Nowadays many electric utilities have this information available on their websites.
There will be three wires coming into the disconnect switch from the utility, two hots and a neutral. Your ground rod will also be connected at the disconnect switch. From the disconnect switch into the panelboard will be four wires - two hots, the neutral and the ground. With this configuration, the ground bus and neutral bus inside the panelboard are NOT tied together.
Your service is 3 wires. Then there is a wire from your grounding system.
The disconnect is a code requirement not a utility requirement. The disconnect is usually the main breaker. Fitting a disconnect between your meter and breaker box may be difficult.