Meter base and sub-panel wiring

uokman · 12-10-2008, 11:14 PM

I am nearing the end of a DIY wiring job on a new construction workshop and am close to making the circuit connections to the sub-panel, running the service line from the main panel to the sub and making those connection.

I trying to research the proper way to do the above a number of questions now exist that I'm hoping someone that know what they are talking about can help me with

Questions:
1). Do BOTH the main service panel and sub-panel require earth grounds?
2). There are 2 terminal block strips on either side of the sub-panel that are tied together with a heavy gauge wire - These are the neutral bars... correct?
3). The other terminal block, I'm assuming is the the ground strip that the circuit wire ground wires connect to - is this correct.
4). How do I know if the bonding screw connection is required or not? Is the bonding screw typically on the ground.
5). What determines wheter I need to use 3 or 4 conductor cable from the main panel to the sub-panel?

Thanks!

kbsparky · 12-10-2008, 11:54 PM

Quote:

1). Do BOTH the main service panel and sub-panel require earth grounds?

Only if the sub-panel is located in a separate building.

Quote:

2). There are 2 terminal block strips on either side of the sub-panel that are tied together with a heavy gauge wire - These are the neutral bars... correct?

Probably. Got a picture for us to look at?

Quote:

3). The other terminal block, I'm assuming is the the ground strip that the circuit wire ground wires connect to - is this correct.

See answer to #2.

Quote:

4). How do I know if the bonding screw connection is required or not? Is the bonding screw typically on the ground.

Sub-panels typically do not use the box bonding screw, provided a proper equipment ground terminal strip is installed.

Quote:

5). What determines wheter I need to use 3 or 4 conductor cable from the main panel to the sub-panel?

For all new installations, you are required to use a 4-wire feeder for any sub-panel. Provided, of course, you are installing 120/240 Volt supply.

J. V. · 12-11-2008, 12:10 PM

Quote:

Originally Posted by uokman

I am nearing the end of a DIY wiring job on a new construction workshop and am close to making the circuit connections to the sub-panel, running the service line from the main panel to the sub and making those connection.

I trying to research the proper way to do the above a number of questions now exist that I'm hoping someone that know what they are talking about can help me with

Questions:
1). Do BOTH the main service panel and sub-panel require earth grounds?
Yes. They both need ground rods too, if the garage is unattached. You also need a ground conductor (EGC) in the feeder for the sub panel.
2). There are 2 terminal block strips on either side of the sub-panel that are tied together with a heavy gauge wire - These are the neutral bars... correct? Yes. You can seperate them and use one for your bare grounds in the sub panel as required. Do not use the bonding screw.
3). The other terminal block, I'm assuming is the the ground strip that the circuit wire ground wires connect to - is this correct.
Yes. It is grounded to the enclosure unlike the neutral bus bar which is insulated from the enclosure. Connect your ground rod to this bar.
4). How do I know if the bonding screw connection is required or not? Is the bonding screw typically on the ground. The bonding screw is required at your service panel. Do not use a bonding screw in the sub panel. You want to ensure that the neutrals and grounds are separated in the sub panel.
5). What determines wheter I need to use 3 or 4 conductor cable from the main panel to the sub-panel?
Use four wires. 3 wires are allowed under the 2005 NEC but that has been changed. It is now 4 wires. That is what you should run.

Thanks!

Have fun and keep us posted.

Gigs · 12-11-2008, 01:19 PM

Please clarify if you are running the actual service conductors to this "subpanel" or if it is on a breaker in the main panel.

From the subject line of "meter base", and your mention of "service line" this is not clear. If it's connected to the service conductors directly with no breakers it's not a subpanel.

uokman · 12-17-2008, 03:14 AM

Sorry for the long delay in responding... Life has been getting in the way of my wiring project the past couple weeks!!!

Let me try to answer all the questions that I created with my original questions...

1) Both (Meter base/main and subpanel) are located in the same building. I believe code calls for a grounding rod at the main service panel which I planned to install.
* - was unsure if the sub-panel, which is located on opposite side of building required a grounding rod as well?
* - Main panel is 200a with a 150a feed to the sub-panel.
* - Planned to isolate the sub-panel with a 150a breaker at the main panel. Main panel has an integrated 200a breaker already part of the box (Siemens)

2) On the sub-panel; the 2 terminal block strips that are tied together (factory Siemens 150a sub-panel) I believe are the for neutral connections.
* - Assuming the sub-panel as described above DOES NOT require a separate ground rod, then I should not bond the neutral terminal blocks?
* I will try to post a picture of the sub-panel later today...

3) Sub-panel ground terminal block; Assuming no additional ground rod for the sub-panel is correct - then the ground wire coming from the service panel is connected to this terminal block in at the wire lug connection AND the ground terminal block is bonded to the box??

4) Electrical service configuration for the building is: Underground Meter Base on outside wall with wall feed-thru to Main Service Panel on interior wall directly behind Meter Base. 200a Service to Meter Base and into Main Service Panel w/200a breaker on Main Service Panel. 150a breaker feeding Sub-Panel on opposite side to SAME building to service electrical demands on that side (A/C heatpump, outlets, lights, kitchen appliances, etc...)
* - I understand that I must run a 4 conductor cable from the Main Service panel 150a breaker to the Sub-Panel. (2-120v legs, 1 neutral and 1 ground) - correct?
* - I am looking at an ~70' run from the Main Service Panel to the Sub-Panel. What is the recommended cable size for that run and should it be copper or aluminum?

I think that got everything!?!

This project has been something else! Next time, I will probably just hire a professional... thought I'd save some money doing it myself but the immense amount of time that I have in the wiring (which has delayed my completion of the building) has been rediculous! However, the meticulous job that I have done on the wiring is worth it in the sense that I have learned a lot, gained a lot of satisfaction in doing it myself and knowing that the job was done (or should I say over-done!) right. This site has been a God-send for me in solving issues that I've run into with some complicated circuits. Thanks for everyones help and input so far!!!

handyman78 · 12-17-2008, 10:16 AM

Quote:

Originally Posted by uokman

*
2) On the sub-panel; the 2 terminal block strips that are tied together (factory Siemens 150a sub-panel) I believe are the for neutral connections.
* - Assuming the sub-panel as described above DOES NOT require a separate ground rod, then I should not bond the neutral terminal blocks?
*
This project has been something else! Next time, I will probably just hire a professional... thought I'd save some money doing it myself but the immense amount of time that I have in the wiring (which has delayed my completion of the building) has been rediculous! However, the meticulous job that I have done on the wiring is worth it in the sense that I have learned a lot, gained a lot of satisfaction in doing it myself and knowing that the job was done (or should I say over-done!) right.

Your last paragraph here is one of the very reasons I do mostly all of my own work. Sure it takes longer but I know it is done by me, no one I have to oversee and done to current codes and expectations. I learn an immense amount about my house and the systems which run it. I too overdo my electrical by placing outlets closer than minimally required, and not trying to cut costs every step of the way. I'm not saying a "professional" always does this but I certainly have seen it done by many as the opportunity presents itself.

Regarding the subpanel terminal strips- they are to be seperated for a subpanel, tied together for a MAIN. All neutrals to one bar, all grounds to the other.

Stubbie · 12-17-2008, 11:27 AM

Why would you have a 150 amp feeder to a garage?

At any rate your siemens mlo panel looks like this image below. You will need to buy a ground bar kit that will install in predrilled swaged holes in the panel back plate as shown in the image. The main bonding jumper is the screw shown just left of the neutral lug on the right side terminal strip. You do not install that screw.

handyman78 · 12-17-2008, 03:13 PM

Stubbie- Looking at your pic of a Siemens panel- (I have the main version of that), I would think that you should be able to use the existing bars if you remove the copper rod joining them at the top (just under the main lugs), to me this would keep the bars isolated as long as the bonding screw isn't being used, allowing the grounds to be on one bar, neutrals on the other.

Speedy Petey · 12-17-2008, 03:22 PM

Quote:

Originally Posted by handyman78

I would think that you should be able to use the existing bars if you remove the copper rod joining them at the top (just under the main lugs), to me this would keep the bars isolated as long as the bonding screw isn't being used, allowing the grounds to be on one bar, neutrals on the other.

The bold part is wrong. You DO need to use the bonding screw for the ground bar. The neutral bar should remain isolated

Stubbie · 12-17-2008, 04:14 PM

Quote:

Originally Posted by handyman78

Stubbie- Looking at your pic of a Siemens panel- (I have the main version of that), I would think that you should be able to use the existing bars if you remove the copper rod joining them at the top (just under the main lugs), to me this would keep the bars isolated as long as the bonding screw isn't being used, allowing the grounds to be on one bar, neutrals on the other.

Yes Siemens provides for that option. You have to purchase the grounding lug kit for the bar on the left. This is the same panel in my previous post converted from split neutral to isolated neutral. I prefer to leave the panel split neutral and add a ground bar for a better wiring configuration.

handyman78 · 12-17-2008, 07:41 PM

Quote:

Originally Posted by Speedy Petey

The bold part is wrong. You DO need to use the bonding screw for the ground bar. The neutral bar should remain isolated

Thanks Speedy I wasn't positive (for a subpanel) so I didn't want to state something wrong. My logic too would be yes, any grounding should include the enclosure, much like grounding any metal box. That being the case, the Siemens box should be grounded using the green screw on the one bar, place all grounds on that bar and remove the jumper. The other would be the neutral bar.

Speedy Petey · 12-17-2008, 08:50 PM

I will say, it is pretty common to remove the bar and bond the ground side, but Stubbie's idea is much better. Leave the joiner bar, do not bond, and add an auxiliary ground bar (or two).
Makes for a cleaner install.

wirenut1110 · 12-18-2008, 06:51 AM

Do you already have the branch breaker for your main panel? I am probably wrong on this but, some manufacturers may not provide a 150 amp branch breaker for your panel.

Stubbie · 12-18-2008, 12:40 PM

Quote:

Originally Posted by wirenut1110

Do you already have the branch breaker for your main panel? I am probably wrong on this but, some manufacturers may not provide a 150 amp branch breaker for your panel.

Good possibility and another rather more technical issue is the panel bus stab rating. For instance a common bus stab rating for a 200 amp panel is 150 amps and 125 amps depending on the manufacturer. This would mean inorder to satisfy the listing, if your bus stab rating is 150 amps then you would not be allowed (technically and listing wise) to install any breakers across from the 150 amp double pole breaker. As I said earlier.. why is the OP wanting 150 amps to a garage??

uokman · 12-19-2008, 01:58 PM

Quote:

Originally Posted by Stubbie

Good possibility and another rather more technical issue is the panel bus stab rating. For instance a common bus stab rating for a 200 amp panel is 150 amps and 125 amps depending on the manufacturer. This would mean inorder to satisfy the listing, if your bus stab rating is 150 amps then you would not be allowed (technically and listing wise) to install any breakers across from the 150 amp double pole breaker. As I said earlier.. why is the OP wanting 150 amps to a garage??

This has gotten too technical for my feable mind!! LOL. The building is a freestanding 40x60 workshop with a equipment bay, office, kitchen and bathroom. (somewhere to live when my wife kicks me out of the "real" house!"

The building will have it's own meter with power in from POCO. The main panel is 200amp. The feed to the sub-panel will come out of the main and be isolated with a breaker.