Ask Me Help Desk - What size of cable suitable

Hello-

I would like some information on wire AWG and grounding requirements with regards to generators. I set up remotely located mineral exploration camps in BC Canada- I am not an electrician... but would like to have some general information, and have an interest in electrical.

Our camps are generally 12-20 man, we commonly use a 10.7 kW (10.7kVA) prime rated diesel generator. Single phase, 240 V, ground and neutral are bonded. The generator has a 50 amp square D series 3 main breaker that is then wired to a Hubbell 50 amp (3 pole 4 wire) receptacle mounted to the generator panel. From the generator receptacle a 200 foot "extension cord" connects the generator to the main electrical distribution panel in camp- power is then distributed from that main panel- 120 volt circuits. The camp is setup and taken down a number of times in one field season, normally the projects are approx. 6-8 weeks in length... so in other words everything needs to come apart easily, wound up, and reused for the next deployment- and is the reason for the 50 amp receptacles/ plugs and flexible rubber extension cord set up.

Presently the generator “extension cord” is made up of a 200 foot piece of 8/4 Carol SJ00W, weather resistant ,4 conductor rubber insulated copper cable. From everything that I have read- 8 AWG is too small given the length and 40 amp draw.

I would like to know:

1. What AWG of cable should be used for an extension cable of 200' long? 250' long? Voltage is 240V; total maximum draw would be 40 amps, but probably much less at any given time. I am concerned about voltage drop, and amperage capabilities of the cable.

2. How should grounding be done at the generators? At the panels? And at any sub panels?
….Presently the generator is grounded via a grounding plate that is connected to the Generator chassis using a bare #4 copper wire (so the entire unit is grounded- the generator is wired so that neutral is bonded to ground). The ground is then continued through the generator receptacle/ plug to one of the conductors of Carol 8/4 cable. (so in other words at the receptacle on the generator there is a ground, a neutral, and two others). At the main electrical distribution panel at the for end of the extension cable- neutral and ground are bonded together, there is another grounding plate that is connected to the panel with a bare #4 copper wire…. If I was to wire a sub panel would I continue to bond neutral and ground at the panel, would I need a bounding plate?

Thank you for any information you have for me.

Since the system is 120/240 volts, the 120 volts is used to calculate voltage drop, and try not to exceed 5% of Vd.

To provide 40 amps at 120 volts 200 foot away ,#4 copper will result in 4% Vd, and 5% at 250 foot.If there are any substantial motor or welding loads, even #4 may not be large enough to keep the Vd reasonable due to any high inrush amps.

Since this system is powered by one generator, the genset is the "service" with the main breaker. The neutral and ground is to be connected, or "bonded" and grounded with a grounding electrode, the plate you mention.

At the remote distribution panel is where the neutral and ground should not be bonded together. The neutral should be on an insulated bar and used only for white neutrals. The equipment ground should be bolted directly to the metal can of the panel, only have the green and bare grounds connected, and the wire from the ground rod/plate that should be at each remote distribution panel.

Did I help you understand this?

Your response did help me understand, a couple follow up comments and a question:

I did not realise that 120 volts would be used to calculate Vd. Though now that have metnioned it, that makes sense.

There are a couple of "smaller" motors: 3/4 Hp on the jet pump, 2 fridge and 1 frezer compressor motors- these I suspect are not considered really substantial single loads. The total of 40 amps would be absolute max (probably never achieved) for many items would bever be in use at the same time.

At 40 amps- ampacity of the cable is not a concern? But rather in this situtation Vd would be. What would the ampacaty be of a #4 200' long? 250' long? Does length play a role in ampacity?

The bonding between ground and neutrel is something I will need to loom at and read more about to understand- I have unstood that they do not get bonded at the remote panel.. but I do not really understand why they are not tied together at the panel.

Thank you for your response- it is very appreciated.

Quote:

Originally Posted by tkrussell

Since the system is 120/240 volts, the 120 volts is used to calculate voltage drop, and try not to exceed 5% of Vd.

To provide 40 amps at 120 volts 200 foot away ,#4 copper will result in 4% Vd, and 5% at 250 foot.If there are any substantial motor or welding loads, even #4 may not be large enough to keep the Vd reasonable due to any high inrush amps.

Since this system is powered by one generator, the genset is the "service" with the main breaker. The neutral and ground is to be connected, or "bonded" and grounded with a grounding electrode, the plate you mention.

At the remote distribution panel is where the neutral and ground should not be bonded together. The neutral should be on an insulated bar and used only for white neutrals. The equipment ground should be bolted directly to the metal can of the panel, only have the green and bare grounds connected, and the wire from the ground rod/plate that should be at each remote distribution panel.

Did I help you understand this?

Ampacity is used as a component of voltage drop calculations, not as a result.

Amps must be know to do the calcs. If the amp is lower the volts dropped would be less.

The volts dropped will be at least noticeable due to the motors starting, but not harmful , for at least short term,since the motors are small. Longterm, I think you take chances of shorting the life of motors. Will all depend on the additional load amps when the motors start.

Can you change and taps or output voltages on the genset? Kicking the volts up will help greatly in keep the volts dropped down also.

Another way is if the genset can output 480 volts, then at remote panels 10KVA transformers 480 V Pri/ 120-240 V Sec can help. Grounding here is different, so let me know if you decide this.

The neutral and equipment ground is only connected at the assembly that contains the Main breaker. If the panel is at or part of that assembly then fine. If the panel you mention is remote, not part of the assembly , keep them separate.

I will ask the generator manufacturer to see if it is possible to change the taps or output voltages of the genset.

I thought about a higher voltage at the generator and the use of a transformer, but though it would be simpler not going that route- and if I ever needed to rent a generator I found that 240 volt rental was much more common.

The panel is remote. As you described "Remote" meaing that it is not part of or connected at the assembly that contains the Main breaker (in this case the genset)... it is remotely connected via an "extention cable".

The remote panel also has a "main" breaker- this breaker is really not required. Would there be anything unsafe or negative with having a breaker at the remote panel?

Just to make sure that I understand correctly- ground would be continues throughout the entire electrical system- Ground at the genset (ground is bonded to neutral at the genset), ground is continured with a conductor in the extension cable to the remote panel, and then the remote panel is grounded- Neutral at the remote panel is not connected to the ground- they are kept separte.

Quote:

Originally Posted by tkrussell

Ampacity is used as a component of voltage drop calculations, not as a result.

Amps must be know to do the calcs. If the amp is lower the volts dropped would be less.

The volts dropped will be at least noticeable due to the motors starting, but not harmful , for at least short term,since the motors are small. Longterm, I think you take chances of shorting the life of motors. Will all depend on the additional load amps when the motors start.

Can you change and taps or output voltages on the genset? Kicking the volts up will help greatly in keep the volts dropped down also.

Another way is if the genset can output 480 volts, then at remote panels 10KVA transformers 480 V Pri/ 120-240 V Sec can help. Grounding here is different, so let me know if you decide this.

The neutral and equipment ground is only connected at the assembly that contains the Main breaker. If the panel is at or part of that assembly then fine. If the panel you mention is remote, not part of the assembly , keep them separate.

Quote:

Originally Posted by FAQ

I will ask the generator manufacturer to see if it is possible to change the taps or output voltages of the genset.

The panel is remote. As you described "Remote" meaing that it is not part of or connected at the assembly that contains the Main breaker (in this case the genset)...it is remotely connected via an "extention cable".

Then the neuteral and ground remain separate, and use a ground rod.

Quote:

Originally Posted by FAQ

The remote panel also has a "main" breaker- this breaker is really not required. Would there be anything unsafe or negative with having a breaker at the remote panel?

No trouble at all.

Quote:

Originally Posted by FAQ

Just to make sure that I understand correctly- ground would be continues throughout the entire electrical system- Ground at the genset (ground is bonded to neutral at the genset), ground is continured with a conductor in the extention cable to the remote panel, and then the remote panel is grounded- Neutral at the remote panel is not conected to the ground- they are kept separte.

Correct.