shop subpanel


  #1  
Old 10-20-03, 07:33 AM
shreveporteric
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shop subpanel

Was at my father in laws house this weekend helping out on a vinyl siding project on his new shop. I noticed something that I thought looked wrong and thought I would post the situation here for feedback.

The electrical subpanel is a cutler hammer 100 amp. the thing I thought was wrong was that his neutrals and grounds were all screwed into the same bar. Further, the panel did not have a grounding rod.

I thought regarding subpanels that: (1) it had to have a grounding rod with a separate ground bar, or (2) the neural and ground bars had to be separated by removing the "connecting screw".

Further, his situation is a little different than most. His shop is in between the power line pole and the house. The city required him to drop power first to a meter base and panel on the shop and then go underground from there to the house.

Another question, does every subpanel have to have a grounding rod or are there circumstances that do not require one?
 
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Old 10-20-03, 07:50 AM
S
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All services to seperate buildings need a ground rod although the main grounding electrode may be buried waterline. You said that the meter was there, this may not be a sub, it may be a service entrance which would be bonded. Is there a disconnect between this panel and the meter base?
 
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Old 10-20-03, 08:26 AM
J
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I agree. This sounds like the main service disconnect where the grounds and neutral are bonded. There should be a ground rods and the panel in the house should be unbonded.
 
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Old 10-20-03, 08:58 AM
shreveporteric
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Yes, between the meter and the shop subpanel is another electric panel with a 100Amp circut breaker for the shop.

Upon another look, I noticted the above menioned panel has a ground connected to a rod as does the meter.

Any thoughts.
 
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Old 10-20-03, 08:05 PM
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He still needs to separate the Equipment Grounding Conductors (EGCs) from the neutrals. Buy a separate Ground buss bar for the panel. Move all of the EGCs to the new grounding buss. Remove the bonding jumper strap or screw that connects the existing neutral buss to the panel cabinet. That will make the setup safe and code compliant.
--
Tom
 
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Old 10-21-03, 06:38 AM
shreveporteric
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Could you please give me a little more info. on the last sentence of your reply. ... remove strap or screw... I think I understand but want to be sure.



Another thing, do we need to go ahead and install a grounding rod?
 
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Old 10-21-03, 07:14 AM
J
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Panels are generally supplied with a green screw or strap that bonds the neutral bar to the frame of the panel. This is optional, and you don't want it.

Each separate structure needs its own grounding rods.
 
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Old 10-21-03, 08:04 AM
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Is the panel fed with 4 wires or 3 with steel conduit? Or 3 with plastic conduit? I think you need more info before deciding to unbond the panel.
 
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Old 10-21-03, 08:21 AM
J
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How true sberry. I saw that Tom had said to unbond so I assumed that a 4-wire feed had already been established. Upon rereading the thread, however, I see that there is no evidence of that.
 
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Old 10-21-03, 09:28 AM
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How many feeder wires?

John Nelson and sberry27 are correct. I did ass/u/me that the feeder from the service equipment to the shop panel is four wires. Please let us know what your actual situation is.
--
Tom Horne
 
  #11  
Old 10-27-03, 01:55 PM
shreveporteric
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Sorry it took so long to reply to the questions raised. I was at the in-laws again this weekend and noticed that there are only three wire coming into the shop subpanel-- two hot wires and a neutral. Again, the circuts that are fed from the subpanel have their neutrals and groiunds tied into the same bar. There is not a ground wire or rod for the sub.

I think there should be a ground rod-- is this correct? Also, would it be better to just run four wires from the main panel and have a neutral bar and and a ground bar. Both could be easily done, which is better?
 
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Old 10-27-03, 03:40 PM
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One more question, is it plastic or metal conduit between the main panel and the sub? The sub may not need ground rods as there should be ground rods for the main panel. In fact you dont want more than one set of grounding electrodes for the same building. Subs within the same structure dont need them. You should get a green or bare number 6 wire and run from the neutral bar in the main panel to a seperate ground bar outfitted in the sub, then remove the bonding screw or strap so you are providing isolated grounding. You want the neutral bar insulated from the panel can and the equipment ground bar in this case.
 
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Old 10-27-03, 04:16 PM
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Equipment Grounding Conductor - Yes. Ground rod - optional.

The correct solution is to add a separate EGC buss bar to the panel and move all of the EGCs onto it. The EGC buss bar mounting screws will bond it to the panel's cabinet. You will connect the fourth conductor that you add to the circuit to serve as the feeder EGC to the new EGC buss bar. After you relocate all of the EGCs to the EGC buss bar you then remove the screw or strap that bonds the original neutral buss bar to the cabinet.

Is the feeder run in metallic conduit or in metal jacketed cable? If it is then you may be able to use the conduit or cable jacket as your Equipment Grounding Conductor (EGC). Just let us know whether the feeder is run in metallic raceway or cable and we can then advise you of the most cost effective way to proceed.

As to the ground rod you do not need one and it can not be used as a substitute for the EGC in the feeder supplying the panel. You are permitted to install one if you attach the Grounding Electrode Conductor from it to the new EGC buss bar. But since it is not required; except in a separate building; I recommend that you do not install one.
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Tom
 
  #14  
Old 10-27-03, 11:46 PM
Vernon Harris
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Shop subpanel

There is some truth in many of the replys. Actually what is correct depends on the state in which you live. While there is a national electrical code, local electrical inspectors can decide some standards on some subjects regrdless of national code. Whether the box requires a grounding rod depends on if the local inspector requires it. Some states only require that the ground rod consist of connecting the ground lug to the rebar located within the concrete found in the footings and stem wall. Others require an actual ground rod. As to whether the ground bar and the neutral should be tied together, again it is the call of the local electrical inspector. Some require that the two bars be connected in all cases. Others require them to be separated except for the main panel. The only correct configuration is to be in agreement with your local electrical inspector. They can tell you instantly what is required. It doesn't cost anything to ask.
 
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Old 10-28-03, 08:36 AM
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There is local code variations for ground electrodes to be sure. We still are not sure if this install used plastic or metal ipe between the boxes. If it was plastic and had 3 wires the bond would have provided for short circuit interuption, but if it was metal and bonded it would been a code violation anywhere.
 
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Old 10-28-03, 12:40 PM
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Vern
Did you read the whole thread? Can you give an example of one jurisdiction that requires the installation or use of grounding electrodes for a feeder supplied panel that is in the same building as the service that supplies it. If you know a place that requires it that will be a new one on me. I have been an electrician for thirty five years and I have worked from Tierra del Fuego to Alaska as well as from French frigate shoals to Uganda. In all that time and all those places I have never had anyone try to force me to install grounding electrodes at a feeder supplied panel located in the same building as the Over Current Protective Device that protects the feeder. I have had idiot engineers try to get me to build a grounding electrode for a system or piece of equipment but they always got upset when I would still tie it in to the Equipment Grounding Conductor that is run with the circuit conductors. The code is more clearly written now but it was never the intent of the CMPs that the earth serve as the Equipment Grounding Conductor.
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Old 10-31-03, 02:18 PM
shreveporteric
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Went back to the inlaws again and noticed that the wires coming into the sub were NOT in any type of conduit. Simply, there were three wires run through the wall. So, with all this said, is it correct to add a ground bar, a ground wire back to the main and separate the neutrals and grounds?
 
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Old 10-31-03, 05:25 PM
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Originally posted by shreveporteric
Went back to the inlaws again and noticed that the wires coming into the sub were NOT in any type of conduit. Simply, there were three wires run through the wall. So, with all this said, is it correct to add a ground bar, a ground wire back to the main and separate the neutrals and grounds?
Eric
The cure for what ails your in-laws feeder supplied panel is exactly as you describe except that all four wires must run in cable or conduit. If there really is no cable jacket or conduit there now the installation is in violation of the US NEC. You can buy the appropriate length of SE cable that contains three insulated conductors and a bare ground at one of the big box stores. If the run is short you could use flexible conduit instead of buying new cable as long as the individual conductors are of a type that is suitable for use indoors and in conduit.
--
Tom
 
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Old 10-31-03, 08:16 PM
Stanthetoolman
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Don't forget the qualified

Some times DIY is a little above the home owner or general "fix-it" person. Sometimes it is just best to hire a qualified electrical contractor to solve major electric issues before someone gets hurt.
We spend many hours in training just to become qualified licensed electricians.
Hopfully you could call a Union shop, I feel we have the world's bests electricians available.
 
 

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