Sub Panel Addition

[JRH]

My home now has a 200 amp main panel with a 60 amp sub off of that out in my detached garage. I only have 5 spaces for breakers left in the main panel and need to install an additional sub panel to be able to wire the basement. Would this be permissible and ok?
Thanks
jrh

[HayZee518]

yeah, two of the five spaces would be taken up by a double pole breaker for your sub panel feed. use a sub-lug panel, with an isolated neutral [no bonding screw] auxillary grounding bar and a four wire feeder.

[JRH]

Please explain what you mean by a sub-lug panel. I have installed a 100 amp 20 space panel. Does the earth ground wire have to go to a copper rod driven in the ground outside or can it hook somewhere to the main panel?
jrh

[HayZee518]

panelboxes are constructed with or without a main breaker. with a main breaker they are bolted by one screw into the metal case and onto the stabs of the bus work.. panels without a main breaker have a set of lugs connected to the main busbars. this is typically called a sub-lug panel. with a sub-lug panel you have the option of attaching your feeder cables to the lugs OR back feeding a breaker fastened over the bus stabs. a sub panel is fed with a four wire seu cable, four wire romex cable with a ground, four wires within a conduit system. the neutral bar in a sub panel is not bonded to the chassis [metal] enclosure. an auxillary ground bus [that you buy] is fastened in intimate contact with the equipment chassis after scraping away the paint. the bare conductor of the cable, romex, conduit system is fastened here. if you wish to drive a ground rod, its connection goes to this aux ground bus.
At the MAIN panel where the sub panel gets its feed, the bare ground AND neutral is connected to the neutral bar WITH the bonding [screw or jumper] connected to the chassis ground and the neutral busbar.
How many spaces do you have in your 200 amp panel? 40?

[JRH]

Thanks HayZee
Now I understand. I already have the sub panel box mounted and it has a main disconnect in it. I prefer it this way then I do not have to cut off all the power if I need to work on something connected in the sub panel.

My question now is- do I need the auxiliary ground to an 8 foot ground rod outside or just use the mechanical ground from the main panel? I am running all wires from panel to panel in pvc conduit.
Thanks
jrh

[HayZee518]

sub panel to entrance

This diagram should help explain a lot of things. The only problem that I see is IF there is a major overload to the panel, the short or overload will pick either breaker to trip. If there were a sub-lug panel, then the breaker feeding the sub-panel would be the one to trip.
NO you do not need a driven ground rod

[JRH]

HayZee, it always looks to me like the regular ground and the auxiliary ground are hooked to the same ground bars. Is there a separate ground bar for the so called mechanical ground lug or auxiliary ground?
My main panel has the small lug for the ground already occupied and no where to do the additional ground. What do I do there?
Thanks
JRH

[HayZee518]

the manufacturer of your MAIN PANELBOX makes a lug that will fit the neutral bus openings so you can fasten a larger cable than the neutral bus will allow.
what is the difficulty in understanding that ONLY in the main box are the neutral and ground connected on the same neutral. In the sub-panel the neutral and earth ground are isolated. look at the diagram!

[HayZee518]

picture

your neutral bus uses a certain kind of screw to hold the wires in it. completely remove one screw and use a thread gauge to find out what the thread is - could be 5/16-24 threads per inch. go to your electrical supply house and get a double cable lug and fasten it to the neutral bus.