Trouble getting MEP-003A going

[Speddmon]

#8 is a bit small for the 003a. If it were regular copper wires, it would be still kinda on the smallish side. In an SO cord or SOW for an 003a you actually need to go to a #4 awg wire size. The NEC has a special de-rating factor for type SO rubber cords, so you need even larger wire than you would normally use.

 

[nostaw]

8-4 SO is rated at 50A / 600v... 10kW is ~52A @ 120v.

Should be fine if I am not running at max capacity all the time.

Would 6-4 be better?

Yes, it would. However it is not necessary for my purposes and a lot more $. This is temporary until I can fund hard wiring and a permanent install.

JW

 

[mistaken1]

Where did you get your 50A rating?

2008 NEC, Article 400, Table 400.5(A) states that an SO cord with three current carrying conductors is rated for 35A.

Your SO cord will work fine for a temporary install assuming you do not overheat the insulation on the cord. As long as the connected load remains at or under 35A the NEC says you wll be fine.

 

[nostaw]

Where did you get your 50A rating?
Your SO cord will work fine for a temporary install assuming you do not overheat the insulation on the cord. As long as the connected load remains at or under 35A the NEC says you wll be fine.

The electrical supply house that sold it to me said it was rated to 50A. I will check the printing on the sheathing when I get home though -- I told them I wanted 50A rated wire. I'll be quite PO'd if they ripped me off.

It is all academic at this point since the generator doesn't run yet, but I'd prefer not to burn anything down once I get it working...

JW

 

[PeterD]

That electrical house was using rule-of-thumb current rating and didn't factor in the fact it was a multi-conductor cable. A single conductor, with free air circulation, will allow higher currents. However, a careful monitoring of temperatures is a valid thing to do. Most heating happens at the ends, at least in my experience. I'm conservative, if it is warm to the touch, I begin to worry and start checking currents carefully. In fact, wire rated at 60 degrees C will feel very warm at its maximum rated temperature.

 

[Speddmon]

mistaken1,

Thank you for posting that page from the NEC. I didn't have time to do it today because of work. All you guys need to remember to read the note under the table in question. The 2 columns "A" and "B", we need to be using column "A" because even though it is a neutral wire, it still carries current by definition because we're dealing with AC current.

As I stated above, you really do need #4 wire to be compliant with the NEC, that wire size would be rated for 60 amps in an SO cord.

 

[treeguy]

Regarding the electrical hook up to the house I was trying to reiterate what I had learned from a conversation with Speddmon. I forget the deatils, but there is something like a direct hook up and an indirect hook up. What I am doing is a direct hook up. Meaning my genny is immediatly attatched to a ground rod, I run 4 wires to a manual transfer switch. In the switch the utility is attached with 2 hots, a neutral, and a ground which is directly connected to the box and the ground comming in from the genny. Flip switch, utility off, 2 genny hots, 1 genny neutral and the all common ground. The 2 hots go to where the utility hots used to be in the main breaker box, the neutral goes to where the utility neutral used to be on the buss bar that combines the neutrals and grounds in the main breaker box. The ground from the Xfer switch goes to the house ground at the main breaker box and connects to the breaker box itself. As a stand alone rig, this is how I understand it to be set up. I have it this way so that I can also run the genny by itself to run my welder. If I am missing anything please let me know. I was just trying to point the OP in the right direction, not knowing his level of knowledge. Thanks

 

[mistaken1]

treeguy

Generally there should only be one location where the neutral and ground are bonded together. (there are exceptions like 250.32 B (1))

If your house has the neutral/ground bond in the meter and not the house panel then a transfer switch that disconnects all four wires requires your generator to have the neutral ground bond. (the generator does not 'see' the neutral/ground bond as it is on the utility side of the transfers switch which is isolated when the transfer switch is in the generator position which sounds like what you have)

If your house is like mine and has the neutral/ground bond in the house panel then the generator must not have the neutral/ground bond even if the transfer switch disconnects all four utility wires as the house panel is where the neutral/ground bond exists. (the generator still 'sees' the neutral/ground bond as it is on the load side of the transfer switch) To run this generator as a separate system (to feed an isolated garage or welder) I would have to re-establish the neutral/ground bond at the generator (as well as connection to a grounding electrode) before using it as a power source.

I think we are all on the same page, just trying to get the terminology to sync up.

The NEC refers to the white neutral wire as the 'grounded conductor' and the green ground wire as the 'grounding conductor'.

A 'grounding electrode' are things like building steel, cold water pipe, driven ground, etc.

All of these grounding electrodes are to be connected together with a wire sized according to Table 250.66 to form the 'grounding electrode system'.

Then the 'grounding electrode conductor' is used to connect the grounding electrode system to the metal enclosures at the building service panel (and ground bus) and is sized according to Table 250.66.

And finally the 'main bonding jumper' sized according to Table 250.66 is used to connect the equipment grounding conductor (bus) to the grounded conductor (neutral).

 

[derf]

I'm not an electrician but I don't think I've ever seen a residential panel that didn't have the neutral and ground buses both bolted down to the inside of the panel, essentially connected electrically.

 

[treeguy]

"I think we are all on the same page, just trying to get the terminology to sync up." --------------- RIGHT

"Generally there should only be one location where the neutral and ground are bonded together." ------------ RIGHT

"If your house is like mine and has the neutral/ground bond in the house panel then the generator must not have the neutral/ground bond even if the transfer switch disconnects all four utility wires as the house panel is where the neutral/ground bond exists." -------------- YES and NO, neutral and ground bond in the primary breaker panel in the house yes, transfer switch disconnects 3 wires comming in from the utility - 1 neutral, 2 hots.

The way I have my house rigged is (just follow along) - there are three wires comming in off the pole/meter one is neutral and two are hot. These three wires will now go into an on/off switch, all three. Then on the other side of the switch are the corresponding three that go into the top of the xfer switch. The bottom of the xfer switch has genny 2 hots and 1 neutral. The house is grounded to the steel water pipe with a bare copper wire. This is connected to the main breaker body, jumped to the xfer body, and jumped to the incomming switch body, and connected to the genny ground which is also attached to an immediat ground rod at the trailer. So then the bottom of the xfer switch output has 1 neutral and 2 hots which the 2 hots go to the main double circut breaker and the neutral output goes to the main neutral buss in the main panel which is also the only point where THE GROUND is attached. The water pipe wire and the genny and the connected box body grounds are all combined and here and only here are attached to the neutral in the main neutral/ground bus bar where all the house grounds and neutrals are together. Elswhere in the house all the neutrals and grounds are seperate. I don't know everything about the internal wiring inside the gennys so if there is a connection with the neutrals and grounds IN the unit, it is news to me. As far as I know there isn't, thats why the rigs have a ground stud on the frame which is jumped to the trailer which I double jump to a ground rod and the ground to the xfer switch. No hard feelings, I love this stuff and if I can learn and share then we're good!

 

[treeguy]

I would also like to appologise to the OP and SS for at this point taking this thread in a total different direction. (pardon the spelling, I can't get spell check to work here)

Also as a note, I regard heavily on what Speddmon has to say, in my book he is the guru when it comes the genny related subjects!

 

[mistaken1]

"I think we are all on the same page, just trying to get the terminology to sync up." --------------- RIGHT

"Generally there should only be one location where the neutral and ground are bonded together." ------------ RIGHT

"If your house is like mine and has the neutral/ground bond in the house panel then the generator must not have the neutral/ground bond even if the transfer switch disconnects all four utility wires as the house panel is where the neutral/ground bond exists." -------------- YES and NO, neutral and ground bond in the primary breaker panel in the house yes, transfer switch disconnects 3 wires comming in from the utility - 1 neutral, 2 hots.

The way I have my house rigged is (just follow along) - there are three wires comming in off the pole/meter one is neutral and two are hot. These three wires will now go into an on/off switch, all three. Then on the other side of the switch are the corresponding three that go into the top of the xfer switch. The bottom of the xfer switch has genny 2 hots and 1 neutral. The house is grounded to the steel water pipe with a bare copper wire. This is connected to the main breaker body, jumped to the xfer body, and jumped to the incomming switch body, and connected to the genny ground which is also attached to an immediat ground rod at the trailer. So then the bottom of the xfer switch output has 1 neutral and 2 hots which the 2 hots go to the main double circut breaker and the neutral output goes to the main neutral buss in the main panel which is also the only point where THE GROUND is attached. The water pipe wire and the genny and the connected box body grounds are all combined and here and only here are attached to the neutral in the main neutral/ground bus bar where all the house grounds and neutrals are together. Elswhere in the house all the neutrals and grounds are seperate. I don't know everything about the internal wiring inside the gennys so if there is a connection with the neutrals and grounds IN the unit, it is news to me. As far as I know there isn't, thats why the rigs have a ground stud on the frame which is jumped to the trailer which I double jump to a ground rod and the ground to the xfer switch. No hard feelings, I love this stuff and if I can learn and share then we're good!

As I understand what you have written all of your metal parts are tied together and connected to ground (should be) and then there is only one place where the neutral is connected to this grounding system and that is at the main panel. That is how it should be.

The question is do you have wire from that ground lug on the generator to L0 on the generator? (a short wire coming from the plug on the back of the AC reconnection box to the grounding lug)

 

[treeguy]

The way that I understand you is that you are talking about the actual genny wiring from the reconnection box to the LO in the output box. Is this the spot that you are suspecting a double connection with ground and neutral? I have read about having to disconnect something in there, that was what I was refering to in my first post in this thread. From what I understand, I don't have to dig into the reconnect wiring harness and disconect something because of what Speddmon said. He said that as long as the UTILITY neutral is disconnected by the xfer switch that I don't have to do this. This is what he was calling a stand alone set up, so you do drive a ground rod for the genny AND run a ground to the house's ground.

You are not talking about having a wire from LO in the genny connected to the ground lug on the frame which is then connected to the genny's ground rod are you?

I have the two hots comming off of the L1,L3 and the neutral on the L0, the ground is on the ground stud on the trailer frame. This also has a wire going to the genny frame and I'm pretty sure there is a wire from that which I'm not sure where it goes. I now feel as though I am missing some piece of info here.

 

[mistaken1]

In stock form the generator has a wire from the ground stud on the frame into the back of the reconnection box where it is internally connected to L0.

If you have this wire in place then you have two neutral/ground bonds in your system.

This is a direct quote from speddmon:

1) At the genset ground lug, disconnect the short wire coming from the plug on the back of the AC reconnection box from the grounding lug and tape it off. (This wire is your L0, Isolate it from ground)

That came from this thread:
http://www.steelsoldiers.com/auxillary-equipment/38439-connecting-mep-house-2.html#post774166

In my personal opinion having two neutral/ground bonds is not the end of the world but it is not what the code calls for. In the interests of safety and protection from lawyers complying with the NEC is a good plan however.

I believe this is the wire speddmon is referring to.

 

[treeguy]

Ok, thanks that spells it out better. Just one thing though, if this wire is disconnected and you want to run a tent city or a welder ONLY, do you need to reconnect that wire we are talking about?

I just looked at mine and the back of that lug has 3 wires. One goes to the neg. on the slave receptical, one goes to the neg. on the starter, and a thinner one goes into the wiring harness into the reconnect box. I am assuming that this last one is the one you'd disconnect.

Regarding another matter, how important is it to follow up on the Army's bulliten about the double ground fault when using the unit as 120V only. I have some tools that I'd like to run 120V only and would turn the settings for 120 to get balanced discharge instead of just pulling from one of the two hots in the 120/240 steeing. I believe that there is supposed to be a wire disconnected/modification to the inside of the reconect switch itself. Finding this wire is going to be complicate or even figuring if this mod. has already been done. Any thoughts?

 

[LuckyDog]

Ok, thanks that spells it out better. Just one thing though, if this wire is disconnected and you want to run a tent city or a welder ONLY, do you need to reconnect that wire we are talking about?

Yes, and ground the genny to earth (a round driven into the ground)

I just looked at mine and the back of that lug has 3 wires. One goes to the neg. on the slave receptical, one goes to the neg. on the starter, and a thinner one goes into the wiring harness into the reconnect box. I am assuming that this last one is the one you'd disconnect.

That be the one...

Regarding another matter, how important is it to follow up on the Army's bulliten about the double ground fault when using the unit as 120V only. I have some tools that I'd like to run 120V only and would turn the settings for 120 to get balanced discharge instead of just pulling from one of the two hots in the 120/240 steeing. I believe that there is supposed to be a wire disconnected/modification to the inside of the reconect switch itself. Finding this wire is going to be complicate or even figuring if this mod. has already been done. Any thoughts?

I would suggest making the effort to see if it was done.

I will let someone else input into just HOW important it is. I remember reading the bulliten, and looking at the updated schematic. I don't remember now a whole lot about my conclusions though.

 

[mistaken1]

Regarding another matter, how important is it to follow up on the Army's bulliten about the double ground fault when using the unit as 120V only. I have some tools that I'd like to run 120V only and would turn the settings for 120 to get balanced discharge instead of just pulling from one of the two hots in the 120/240 steeing. I believe that there is supposed to be a wire disconnected/modification to the inside of the reconect switch itself. Finding this wire is going to be complicate or even figuring if this mod. has already been done. Any thoughts?

I do not have an answer for this either. If a bulletin was put out it must have been put out for a reason so I would say we all need to do it (or verify it has been done) if we are going to run our generators at 120V single phase only.

 

[mistaken1]

Here is a great explanation and diagrams of a generator hookup.

From this site:
Generator Grounding

I copied the information from electrical design tutor and uploaded it as a pdf here:

http://www.steelsoldiers.com/auxill...onductor-house-panel-question.html#post929555