sub panel

[myvalk]

running juice to my new addition.
putting in a sub panel, feed by a 50 amp fuse from the main panel tha used to power the electric raange.
question is.. does the sub panel need a main breaker? i hope not, i bought and installed a 8 - 1/2 inch or 16 - 1/4 inch breaker box.
thanx
oh yeah.. does the ground need to have a rod to the earth? no problem if it does.
im in new york by the way.

[bkrahmer]

You don't need a main breaker in your subpanel, but they can be nice to have.

Make sure that you isolate your neutrals and grounds in your subpanel. The neutrals must go back to the neutral bus on the main panel.

As for grounds, I've heard both ways. I have a subpanel in my shed with the ground going back to the main panel ground, and I haven't noticed any problems. Having the subpanel grounded with a rod is probably a better route to go, however.

[Sparks]

The only reason you would ever need another ground rod would be if your addition was a separate building. Any separate structure or building that has more than one branch circuit would need a ground rod. I'm assuming your addition is attached so you wouldn't need one. Ground rods are mostly for lightning and utility spikes hence the requirement for separate buildings. Again, make sure you use a 4 wire feeder to your sub, and just like already mentioned, isolate the grounds from the neutrals meaning don't install that green bonding screw and sometimes this means you will have to purchase a separate ground buss kit on which to terminate your ground wires. Good luck.

[bkrahmer]

That makes sense. Thanks for clearing that up for me, sparks.

[myvalk]

im still a little fuzzy on the facts.. ill try to re read it .
thanx

[Sparks]

myvalk, that's understandable. It takes years of study and experience to grasp a lot of the concepts relating to electrical safety that's why there is so much misunderstanding of the NEC and the trade itself. Regarding the 4 wire vs 3 wire, the intent here is to NOT create a parallel neutral return path. This is more dangerous when you're using metallic conduit for a raceway. If you connect the neutrals and grounds together in a s ub-panel, you are giving neutral current more than one path to return to it's source (the utility transformer). Contrary to popular opinion, electricity returns to it's source, not to ground. When you allow neutral current to return on let's say metallic conduit, just say some load is active on the sub-panel so there's current returning on the conduit (if improperly wired) then some unknowing person decides to loosen a fitting on the conduit and just happens to touch the breaker panel and that conduit or fitting (conduit pulled out) putting himself in series to the reurn current. Well it only takes I believe 2 milliamps to create cardiac defribilation and you have say 7 amps returning. Current flowing through heart.That is only one example of what could happen, there are many. Just always remember one simple fact, the neutrals and grounds should only be connected together (bonded) in ONE LOCATION, this location is the main disconnect, usually your main panel (not always). They should never be bonded anywhere on the load side of the main service. (handymen are notarious for this) You never want neutral return current flowing on ground wires, conduit, water pipes, gas pipes, building steel, kitchen faucets, etc, and this is what can happen if sub-panels are not wired properly, combine that with a loose ground wire or fitting or bonding clamp and you could have arcing and a fire as well. Potentially deadly in more ways than one.

[myvalk]

very well explained, sparks.
so in the sub-panel, ill keep the grounds together, and the neutrals together, but not grounds and neutrals together.... right?

[Sparks]

Correct. Make sure the neutral bus does not get mechanically connected in any way to the enclosure. Depending on manufacturer, you may have to purchase a separate ground bus kit, which of course will be mechanically connected to enclosure and not connected to neutral bus. (again, don't install the bonding screw or strap that you will receive in the package) These would only be installed if panel was being used as the main service panel. Although there are some panels that you would install bonding screw or strap in ground bus only, it depends on panel. Just make sure ground bus is mechanically connected to enclosure and that neutral bus is not mechanically connected to enclosure, and again, keep everything separate. Good luck.

[myvalk]

thanx again for the info.

[Sparks]

No problem.

[porcupine]

Sparks is right. Seperate the ground from the neutral. Alot of the panels have a bar running behind the the main (under a plastic piece), connecting the two neutral bars, that can be removed by disassembling the bussbar, then once you reassmeble the bussframe (without the neutral tie) you can designate one side as a ground, and bound it with the ground screw.
Or you can buy a Square D QO subpanel, and that has an unmounted buss detail packaged with bound screw and lying in the bottom of the box.
Good luck

[Emer Construction]

I don't understand why the neutrals and grounds at the main panel have to be on seperate bars then bonded together. Why can't they just go to the same bar? I see it in other panels, but my inspector doesn't allow it.
Sparks ?

[Sparks]

Without pulling the code book out, I don't believe this is a nec requirement for main service panels, just sub-panels. Some inspectors will enforce this citing "work shall be done in a neat and workmanlike manner". I always like to put them on separate bus bars anyway. I hear ya though, I've seen it done both ways as well.

[porcupine]

Emer,
It' simple, your main panel is bonded to an earth ground AND a water main ground. If someone removes the bond screw at the main(or just never installed it), and your relying on that continuous bond at your sub panel, your enclosure (box) could become neutral "hot", especially if something happens to the neutral from the service entry (like it disconnected from the pole). Your main panel enclosure would be isolated from this, because of the removal (or lack of) of the bond screw.
If you've ever received a neutral "feedback" shock, you'd know that it could feesibly kill you.
As for your inspector, he's probably just a d&@k, and wants things done his way. I don't think the the NEC has a code against the intermingling of grounds and neutrals in the main service panel. However your local code may. I work in New York City, one of the most stringent local codes (we,re not even allowed to use 1/2" conduit for line voltage) in the country, and we have no such code that I know of. If your inspector doesn't allow it, ask him why. You could also contact your local town hall, and ask them for a copy of your local electrical bonding code for main services. Best of luck.