Revisiting the PTO-generator question

[Trev]

Thanks, Spence! Great info and links... I'll keep them for when I meet with our electrician.

<font color=blue>I only have a 7500 watt rated, 10000 watt surge portable generator so a 100 watt or even 60 watt switch would have been enough.</font color=blue>

But, doesn't the switch also have to be rated to handle the full load from the power company as well? You can't just get one rated only for the generator, can you? I have a 200-amp service coming in, and my switch would have to handle at least that, plus some safety headroom, correct? Or am I, as usual, missing something?

Thanks again,
Bob

 

[djradz]

Even though the generator may only serve a portion of the load, the switch must be rated the same as the service. When the generator is not in use and the normal supply is from the utility, the switch could see up to the maximum of the service panel in load. Also, I am not sure the neutral needs to be switched. Someone should address the tying of all three neutrals together permanantly. This may be acceptable.

 

[Spencer]

Ah yes, you are correct old wise one. I knew there was another reason I wanted at least a 200 amp switch. Thank you for catching my error before someone else caught it and ripped me a new one.

 

[Spencer]

djradz,
In the event that power lines have been downed, their neutral wire could come in contact with other wires couldn't it? Thanks for pointing out my switch rating error without making me sound like an idiot.

 

[Anonymous Poster]

Neutrals-
There are a couple reasons for isolating the Neutral when switching to generator; One of witch you already figured out, the neutral from the power company could easily be in contact with a hot wire someplace down the road. The neutral is always the top wire on the pole in secondary circuits on the pole, so it's easy for a neutral to short when a limb falls on it. I don't know why the Neutral was so positioned back in the early days of utility standards, I ain't that old, but I do know anyplace I go in America the Neutral will be on top.
The second reason for isolating the neutral is because there is often voltage above ground on the neutral. This occurrs for a lot of reasons, including flourescent ballasts, and inductive loads, and needs to be dealt with.
Even MORE Important in generator installations is GROUNDING the genset. The first connection made when hooking up the generator should be the mechanicle ground. Did you ever notice the GROUND prong on an electrical plug is longer than the others, so ground connects first.

 

[Trev]

<font color=blue>Even MORE Important in generator installations is GROUNDING the genset. The first connection made when hooking up the generator should be the mechanicle ground.</font color=blue>

In the case of my PTO generator, I would assume this would entail actually having a ground strap bolted to the machine, and a copper rod that is pounded into the ground before the machine is used?

They should come with those, if that's the case.. wouldn't you think? Is there any specific specs that need to be followed, e.g., how heavy the wire is, how deep you pound the rod, etc.?

Thanks, yet again..
Bob

 

[gerard]

I used a standard 6 ft ground rod that I bought separately, drove it into the ground near where I run my generator, and ran some copper wire to it that I keep rolled up unless the generator is being used, then I just connect it.

 

[Anonymous Poster]

The grounding conductor should be of equal size to the current carrying conductors.
May I humbly suggest bonding the genset ground to the distribution of the electricity, be that breaker box or whatever.
You'd be surprized at the resistance that can occurr between a ground rod and another one 10 feet from it. You may not see it on your VOM, but I assure you it shows up on my Null Balance megger. Ground problems can get both expensive and dangerous real quick.

 

[John_Mc]

<font color=blue>Even MORE Important in generator installations is GROUNDING the genset.</font color=blue>

Any reason you couldn't just clamp on to the same ground rod the main power into the house uses? The generator receptacle on my house is right near one of these rods. I've been trying to think of a situation where using the same rod would be a problem, and so far have not come up with one.

 

[Anonymous Poster]

Clamping onto the existing ground rod would be the second best way to do it. Best would be connecting to the ground bus in the breaker box, where the wire from your ground rod connects.