Generator amperage

[wayne123]

Just installed a manual generator panel in a customers house. I fed the panel just like a sub panel and tied in specific circuits that they wanted to use in case of a power outage. Its a 60 amp Sq D generator panel with an interlock on two 60 amp 2 pole breakers that will not allow both breakersa to be on at the same time so there will not be any backfeed. After i had all the circuits tied in and the power was on to the panel I checked the amp draw which was approx. 8 amps on the feed conductors. When I hooked up the genrator to test the system the amperage from the generator to the panel was 17 amps with the same loads connected. Whats going on here?

 

[caj1962]

Re: Generator amperage

Just a guess but the amperage doubled that should indicate the voltage is only half of what it should be or was to start with. Make sure you are not tieing the nuetral from the generator to a phase conductor conection.

 

[wayne123]

Re: Generator amperage

Did that. I have 250 v on the generator line.and 130v H to N and H to G.

 

[hurk27]

Re: Generator amperage

If there is resistive loads (like in in incandecent lights) and you increase the voltage (from 120 to 130) the current would also increase but I dont think this much even at a 4 to 1 ratio but it does work out close. I think when you increase a heating load the current jumps by 4 times. but I'm too tired to get into the figuring.
Also it sound's like this generator is maybe over speed this would also throw the frequency off too.

 

[wayne123]

Re: Generator amperage

Is the speed adjustable on a portable generator. I know the voltage was a bit high but still withen tolerance.

 

[charlie b]

Re: Generator amperage

There?s another possibility, but first three questions:

(1) Is the transfer switch a 3-pole (i.e., does it switch the neutral)?
(2) Is there a ground rod at the generator, and is it bonded to the generator?s neutral?
(3) Where and how did you connect the neutral from the generator to the neutral of the sub-panel?

IF your answers were
(1) No, and
(2) Yes, and Yes, and
(3) Bonded to the sub-panel?s neutral bus,

THEN the extra current might be flowing through a parallel path that includes the sub-panel?s neutral bus, the main panel?s neutral bus, the main panel?s ground rod, planet Earth, and the generator?s ground rod.

This would be an improper connection. If the transfer switch does not switch the neutral, then the generator does not create a ?separately derived system.? The generator?s neutral and its case should not be bonded, and an EGC needs to be run from the main panel to the generator?s case.

[ December 12, 2003, 11:35 AM: Message edited by: charlie b ]

 

[wayne123]

Re: Generator amperage

1. No
2. No ground rod. No bond.the generator should have this bond. Correct
3.Neutral from the generator is bonded to the Neutral of the sub panel which is connected to the Neutral of the main panel. The egc and the neutral are not bonded in the sub panel

 

[wayne123]

Re: Generator amperage

Charlie, does the generator need to have it's own ground rod or can the egc in the main panel suffice?

 

[charlie b]

Re: Generator amperage

We might be on to the problem here. Let?s be clear about a couple things. Generators are generally constructed with an internal bond between their neutral point (i.e., the center tap of the generator windings) and the case. If you don?t create a separately derived system (i.e., if the transfer switch doesn?t switch the neutral), then you need to do two things. One is to disconnect the bond (neutral to case) that is internal to the generator. That is because the generator would not meet the conditions of 250.34(C). The other is to run an equipment ground conductor from the main panel to the case of the generator. Otherwise, there would be no way to satisfy 250.4(A)(5).

If you didn?t do both of these two things, then the current path I described earlier might still be present. Even without a ground rod at the generator, there may be sufficient contact between the case of the generator and planet Earth to permit current flow, just from its sitting on dirt or on a concrete pad.

As to a ground rod at the generator, yes you need one. This is because the installed configuration would not meet the conditions of 250.34(A).

 

[wayne123]

Re: Generator amperage

Thanks, Charlie.I will drive a ground rod and check to see if the N is bonded to the gen.case. I will let you know how it turns out.

 

[brian john]

Re: Generator amperage

Not sure of the type of loads you?re feeding but loads change.

Are any of the loads thermostatically controlled?

Did someone or something turn something on or off?

The ground rod may make a difference with the neutral current but load current should not be affected.

Was the load 8 amps per leg? The 17 amps, almost doubling might be a clue.

What is the current on line 1 and line 2 what is the neutral and ground current?

What is the voltage line to line, line 1 to neutral, line 2 to neutral, neutral to ground and line 1 and line 2 to ground?

 

[tom baker]

Re: Generator amperage

Most large generators do not have the neutral bonded to the generator frame, by large perhaps 10 KW and larger. Some generators with on board receptacles will have an internal bonding jumper from a receptacle neutral to the frame, I took one apart once, I just had to know.
I researched the larger generator neutral grounding connnection a while ago, check with the several mfgs it seems the most common is not to bond the neutral.
But, it can be either way, and you need to check.
Here is a thought: UL now has a generator standard for stationary generators, UL 2003 or something. Does anyone know what it specifies for grounding of the neutral?

 

[hurk27]

Re: Generator amperage

Tom
We have three Coleman 5 kW generators that have a bond at the 120 volt receptacle. It also has a 4-wire 120/240 receptacle too and a switch to change which receptacle that is used. when the switch is in the 120/240 position the neutral bond is no longer tied in and the EGC on the 4-wire 120/240 receptacle is bonded to the frame. The manufacture even states to use a two-pole TS when using the 240 receipt in the instruction book.
If you can picture a three pole double throw switch with one of the poles has the commons going to the frame bond when the switch is in the 120 volt position this pole in the switch connects to the neutral going to the 120 volt duplex, when it is in the 120/240 position it connects to the green wire going to the grounding terminal on the 120/240 4-wire receptacle. The other two poles are used to switch the two hots.

[ December 13, 2003, 02:30 AM: Message edited by: hurk27 ]

 

[karen]

Re: Generator amperage

The generators I have worked on in marine applications all have the neutral bonded to the generator frame, up to 100kva.

 

[wayne123]

Re: Generator amperage

Maybe the problem is that since the TS doesn't switch the N and when I tested the installation I did not turn off the rest of the circuits in the main panel,I was possibly getting some feed back from the main N. This situation will not occur when there is a power outage. I really am concerned about taking the bond to ground off the the generator because this is a portable generator and he uses it around his farm to do fence work etc.and it may cause a shock hazzard. Also I am concerned that it might void the warranty on it.

 

[lady sparks lover]

Re: Generator amperage

Question, do you have to use the 125% (MCA) multiplier for Generators since it is the motor, or since the Generator will wind down do you treat it as a normal load when it's out of fuel??