another stupid sub-panel question

[John Onofrey]

What is it with sub-panels?

I got two main service panels with a sub-panel. Three wires feeding sub-panel and ground and neutral bars are bonded. The 100 amp feed to the sub-panel has a marker on the wire that says gen-set and the 100 amp breaker on the sub-panel attached to the feed says sub-panel feed. This is on the left side of the sub-panel. The right side of the sub-panel has a 60 amp breaker labeled portable gen. receptacle. There is a twist lock receptacle in the garage presumably for a portable generator.

I can't tell of course if they intended for a genset with a transfer switch to be inserted between the main panel and sub-panel (this would seem to make sense). There are two boxes on the side of the house about six feet apart that have what appears to be about #6 AWG wire in them but they are not connected together in anyway. You would think that without the generator, they would need to connect the ends of these wires together temporarily. The receptacle marked as for a portable generator doesn't seem like a good idea. If your using that, what happens when commercial power kicks back on? Do portables come with some kind of sensor so they kick off when commercial power is restored.

Any thoughts?

[Jeffrey R. Pope]

Where is the service disconnect John? I don't see it.

If it is anywhere other than in one of the panels you've pictured, these would all be "sub" panels (distribution or load side panels).

The "GEN SET" appears to be a separate panel all together (back-fed from a generator supply). Did you check for current at that panel?

[bkelly1]

Good generators come with a transfer switch. Was there one on the property. I have seen some models where you can put the rotation the same and let her go. But not often. Or, maybe that was soemthing else. Was there a transfer switch?

[John Onofrey]

Sorry, I got distracted and forgot to come back here. No generator on site. Recepticle for portable in garage that connects like a branch circuit to the sub-panel.

Two, 200 amp disconnects on right side of structure. The sub-panel was fed by one of the main panels. I figure the theory is that in the event of a commercial power failure, you are supposed to shut off the feed to the sub-panel and then power up the gen-set, this will feed the sub-panel branch circuits. When commercial power is restored, turn of the gen-set and turn on the breaker that feeds the sub-panel.

The heavy gauge wires in the boxes on the other side of the house are for future barn and pool.

Thanks for your help with this one.

[Richard L. Bennett]

All

Sometimes a posting of a one line electrical diagram would help

sometimes it takes less effort that trying to explain it in english

rlb

[hmiller]

Originally Posted by jonofrey

I figure the theory is that in the event of a commercial power failure, you are supposed to shut off the feed to the sub-panel and then power up the gen-set, this will feed the sub-panel branch circuits. When commercial power is restored, turn of the gen-set and turn on the breaker that feeds the sub-panel.

John
What I can see appears as you have described it. Normally one of the main panels supplies power to this sub panel, that can be switched off and locked out when switching on the generator supply, and vice versa. Of course they could have use a commercially available manual transfer switch, like Gen-Tran.
I assume you already suggested review by a licensed electrician, or the local electrical inspector.

[Jeffrey D. Clark]

I hope it was done by a qualified electrician using a real transfer switch. I've heard stories about Joe homeowner backfeeding the utility during an outage. Suddenly step down transformers become step up, putting linemen working on the outage at risk.

[Greg Fretwell]

It is certainly possible to backfeed the grid with a portable generator but that is fairly unlikely. When your little generator hits the locked rotor of your neighbor's HVAC it will usually trip the generator's breaker.
That still does not relieve you of the legal responsibility to have proper transfer equipment. If the power company does catch you backfeeding the grid they will probably cut your drop and be pretty slow getting back to hook you up.

[hmiller]

The other problem with backfeeding the grid is that when the power comes on, I don't think you generator is going to fair real well.
I have never tried it, but I would have to assume that this pretty much ruins the generator. ? Anyone know?

[Greg Fretwell]

Again it will probably just operate the O/C protector but you will be dealing with a higher available fault current than the breaker in a generator and perhaps the one you are backfeeding, is rated for. It is possible that it might just weld shut.
It will take more than one failure to cause a problem but in a storm situation people can get careless.