got my pto-generator today.

Inspector507 · Sep 14, 2004

Tom,
They're both going to do the same thing, disconnect the ungrounded conductors from the supply. There's no much chance of getting feedback since the neutral is normally a non-current carrying conductor. Most of building here that we inspect have a solid neutral connection. Once in a while we'll see a derived neutral from a genset, but rarely. That also causes a grounding nightmare for the installer.

I think what may be the "unsafe part" about using a cord to connect through an outlet, would be forgetting, just once to shut off the main. Besides the fact that if you are using a double male cord, thats dangerous as well.

Soundguy · Sep 14, 2004

I'v been lurking in my own post /forums/images/graemlins/shocked.gif /forums/images/graemlins/tongue.gif

So basically what we have come to the conclusion is.. that someone who powers their whole house , for instance, thru a dryer outlet and a double male cord, and who -does- turn off the main breaker, is doing this safely.. in respect to any lineman working on the lines.. but it is unsafe in the respect that if you forget to turn the main off bad things happen, and the inherant shock hazard of a double male plug.. I get that right?

Soundguy

Inspector507 · Sep 14, 2004

Basically yes

SPIKER · Sep 14, 2004

I haven't been on in a few days:

Inspector57 seems to have most everyone straightened out.

think of a generator disconnect switch as a two pole switch with 2 blades, which has TWO throws, the house is tied into the center of the two blades, toss the switch to the TOP it connects the 2 hot leads to the electric grid, , pull the handle DOWN and it ties the house to the generator... the N does not get disconnected, the Generator HAS to be grounded by BONDING it to the house ground rod @ same place HOUSE is grounded at. otherwise there is a ground diferance bewteen the generators mounting spot and the houses ground point. the N of the generator is usually (but not always) bonded to the Generators frame. but also needs to be connected to the hous's N wire.

in regards to an out building: if running power from an inside house panel through a breaker in that panel to power the shed or out building with/for 220 volts AND 120 volts. THEN you need a sub panel in the shed. AND you HAVE to run 4 WIRES to that shed and tie the GROUND to the GROUND HOTS to HOTS and N to N. BUT you can not tie the N to the G in the SUB-PANEL. you HAVE to run a NEW GROUND ROD at the shed. this is not concrete though and in some cases can be run using only a 3 wire system depending on type of flooring in the outbuilding. if it is a Milk parlor or swimming pool then there is additional ground rod bonding systems that are required... these are usually a coated re-bar system run along with the footers and burried so that there is 100% continous loop surrounding the pool/parlor or not tub. also a few other factors that can come into play. mostly being the local inspector and any additional codes.!

(yes one inspector will choose to inforce one part and add his own thoughts/codes into the mix which may or may not have true CODE backing but one village/city will and or can have different codes that THEY must follow...)

I don't think OUR inspector57 will disagree with that last part much! too many towns think they KNOW better as to HOW to do something, the NEC is basically a REFERANCE as to what the bare minimum should be...

Oh I won't even start on the codes for hospitals and O2 storage locations or places with HALON fire suppression systems! /forums/images/graemlins/blush.gif

MarkM

MicroPilot · Sep 15, 2004

( ....in regards to an out building: if running power from an inside house panel through a breaker in that panel to power the shed or out building with/for 220 volts AND 120 volts. THEN you need a sub panel in the shed. AND you HAVE to run 4 WIRES to that shed and tie the GROUND to the GROUND HOTS to HOTS and N to N. )

The 4 wires being 2 120v hot legs, a neutral, and a ground?

( BUT you can not tie the N to the G in the SUB-PANEL.)

I'm assuming I've got the 4 wires correct as above, where does the Gnd wire from the house panel go in the sub panel? The ground block?

( you HAVE to run a NEW GROUND ROD at the shed. )

Wouldn't this new ground rod ALSO be connected to the ground block in the sub-panel?

( this is not concrete though and in some cases can be run using only a 3 wire system depending on type of flooring in the outbuilding. ...)

3 wires being Hot, Neutral, and Ground?

What are the implications of not having a ground from the main panel going into the sub-panel?

SPIKER · Sep 17, 2004

(

The 4 wires being 2 120v hot legs, a neutral, and a ground?

YES

I'm assuming I've got the 4 wires correct as above, where does the Gnd wire from the house panel go in the sub panel? The ground block?

YES> there is typcally a Jumper or a Connector that connects the N Buss bar to the G buss bar, that JUMPER has to be removed, and the Panel Ground is bolted to the sub-panel. the N then is only connected to the Main House Panel's N, NOT to any of the ground paths in the barn/shed.>

Wouldn't this new ground rod ALSO be connected to the ground block in the sub-panel?

YES ground rod & ground in the sub-panel.
3 wires being Hot, Neutral, and Ground?

What are the implications of not having a ground from the main panel going into the sub-panel?

>the implications then are that there can be a potencial voltage differance between the EARTH out in the distant barn/garage and the G recipticals wire ground. < rembember the saying "Ground is not GROUND the earth around," this is an old electricians saying which basically means that if you stick a ground rod into the ground at point A, and run wires 100's of feet away, you can actually measure a + charge between the G wire and the actual earth out away from the ground rod... (there is Resistance in the earth, put in a ohm meter set it to resistance and stick one lead into the dirt, move the other lead as far away as possable and push it into the dirt. you will only measure the amount of resistance from those 2 points to each other. this resistance will change as water levels change and as the dirt comasition changes... wet clay is better at conducting than dry hummus...

)

this is primary reason for adding the ground rod @ an out building and sepperating the N and the G inside the SUB-PANEL @ that location, the codes do not know if the garage is 10 feet away, 100 feet away or 1000 feet away. so reason for seperating the G 7 N is that the N is meant as a return path for power, the G is not. the 2nd ground rod is susposed to tie the two buildings together by Location rather than by RESISTANCE of earth. I'm not 100% sure WHY they want the N & G sepperated @ the sub-panel, to me I think that COULD cause a Floating Voltage on the N vs the 2nd G location IF something were to happen to the G wire that is running between the 2 buildings... (remembering that the G & N are tied together in the MAIN PANEL)

this MAY have something to do with the GFIC requirements, for any building with out a finished floor and or dirt floor or below grade with a concrete floor or with a garage type location where vehicals are stored..... (wet cars/tractors in a garage means higher chance of electrical problems between YOU and the dirt.)

hope that helps.

oh BWT: MY DISCLAIMER
I'm not a pro electrician, I DO a LOT of it and have been doing INDUSTRIAL electricity for years, and have an electronic engr degree but no licenceing, have thought about getting my state licence for electrical and HVAC but just have not had need to do so. I DO keep up on the codes, but only the NEC not any local ones... /forums/images/graemlins/crazy.gif

Mark M

rswyan · Sep 17, 2004

( this is primary reason for adding the ground rod @ an out building and sepperating the N and the G inside the SUB-PANEL )

Ok, don't want to steal this thread ..... I got a couple of quick questions.

I'm not an electrician by any means but I have done a little wiring (adding circuits off a panel, etc.) Here's my situation:

I have an outbuilding/workshop located approximately 450' or so from the house. It is well constructed (masonary block) but as I have gradually added more tools & equipment it has become kinda small. The location of the shed is not ideal for a variety of reason (distance from the house and the fact that it sits in front of our house) Latest interest is to add a MIG welder (probably around a 210/250 size-wise)

The electric is 208/220/240 (whatever) fed from the house via three large aluminum multi-strand wires (dunno what gauge exactly but they are about as big around as my pinkie) There is an 80 amp subpanel out in the shed. As far as I can tell, there is no ground out at the shed (just neutral back to the house) Should there be ?

Also - anybody have any thoughts about that long a run of aluminum wire ? I run lights, powertools (bench grinders, small metal bandsaw) and a small (5hp) compressor out in the shed off this feed. I was having occasional trouble with the compressor tripping the breakers until I moved it over to a pair of 20 amp breakers on the subpanel (it had been on a pair of 15's) A friend and I tried hooking up his Lincoln stick welder out in the shed when I needed some welding done - didn't work worth a hill of beans. I'm just guessing but apparently the current loss was so great that it wasn't getting enough juice.

Any help appreciated.

Inspector507 · Sep 17, 2004

I think you're correct the length of the run and the aluminum conbined to make for a situation that will not be good.
Probably when the garage/barn/shed was wired, the code requirements were different than they are today. There have been changes every 3 years for this situstion for a long time.

johnbilt · Sep 17, 2004

Hi

I have a similar set-up for my shop, although it is only a 150 foot run. Your 450 ft is a long run and voltage drop is an important consideration.

If the AL wire is the size of your pinky, then I will guess it is a 1/0, at best. Regardless, The size must be increased to supply the current you need to drive a large load such as a welder.

If you run a feeder panel out to your shop, 3 wires are fine, but you must install a ground rod system at the shop panel, and connect the neutral to the shop ground at that point.

The other option is to run a 4th wire for ground, properly sized for the fault current. It is probably cheaper and more practical to install the ground rods with the 3 wire system.

Assuming a maximum of 2% voltage drop over 450 ft, for a 240V ckt at a 50A load (welder ckt):

240V * .02 = 4.8V Drop Max

4.8V / 50A = 0.096 ohms Circuit Resistance Total

My table shows a 2/0 CU or 4/0 AL would be a bare minimum for this run at 2% drop.

A 300mcm CU would be a better choice keeping the voltage drop to 1%.

Remember that AL wire is cheaper, but must be approximately doubled in size to get the equal performance due to the resistance.

When the cost of wire gets too high, you may consider asking the power company to give you another service drop at your shop.

Disclaimer: Please check with your local power company and electrical inspector before proceeding with any work. Safety is the most important consideration over money. You won't be able to enjoy your shop if they have to bury you while trenching in the new cable. /forums/images/graemlins/grin.gif

Good Luck

John