| Author |
Message |
jimbo
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, June 28, 2005 - 6:15 pm: | |
Need some advice concerning 120/240 wiring, especially bonding of ground and neutral at genset panel.
Recently acquired 120/240 V Power Tech 10kw genset for 1977 Eagle Motor Coach. Local installer stated that the genset only puts out 120 V "because the voltage regulator is wired for 120 V." However, a voltmeter across the two 120 V output leads from the genset to the genset panel measures 240 V. I was under the impression that this reading should be 0 V if the output was only 120V.
Genset has 1 dipole 50 Amp Breaker. 2 leads from breaker go to separate genset panel along with ground and neutral. Ground and neutral are bonded at genset and genset frame is grounded to chassis. Ground and neutral are also bonded at genset panel and genset panel is grounded to chassis. Genset panel has three 30 Amp breakers that feed three separate 30 Amp female sockets (1 for front air conditioner, 1 for rear air conditioner, and 1 for coach 120 lights and appliances). Front air conditioner and coach circuit feeds from one 120 V lead from genset, rear air conditioner feeds from the other 120 V lead from genset.
Coach 120V system has separate panel. Ground and neutral are isolated (not bonded) in this panel. Ground is bonded to panel and to chassis.
My confusion: Should the ground and neutral be bonded at the genset panel? I was told that they should be bonded within the genset itself, but nothing has been said about bonding at the genset panel. It seems to me that the genset panel should be configured just as the coach 120V panel (that is, ground and neutral isolated within panel and panel being bonded to ground and chassis).
My thinking (may be flawed....would like some expert input):
Since 240 V appears to be coming from the genset on 2 separate 120 V lines, the 240 V is regulated and the lightly loaded line will deliver a high line to neutral voltage and the heavily loaded line will delier a low line to neutral voltage. The loads on the separate 120 V lines would always be out of balance (front ac and coach appliances vs rear ac or no ac) and so the neutral would potentially be carrying a high voltage. If this is the case and if the neutral and ground are bonded at the genset panel and the panel bonded to the chassis, would this not result in the skin of the bus being live with a potential dangerous voltage? And if the skin is hot, OUCH????
Jimbo |
Richard Bowyer (Drivingmisslazy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, June 28, 2005 - 6:46 pm: | |
Most gensets are wired using a 120 volt voltage regulator which senses one leg of the 120/240 volt output. What is the regulator. Typical is a Basler VR-63 or similiar.
As long as the loads are balanced within about 20-25%, the output voltage will remain within the tolerences. 120 volts on one leg and 110 volts on the other leg to neutral will not cause any problem.
If desired, the output can easily be rewired for straight 120 volt output. This is what I would do if I did not have any 240 volt appliances.
Richard |
John that newguy
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, June 28, 2005 - 6:51 pm: | |
An owner's manual is here. |
Jtng
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, June 28, 2005 - 6:55 pm: | |
Even without 240v appliances, it might be better to use a "two leg"
120v system, that way, when one circuit trips due to an overload,
you'll continue to have power to the other circuit. |
Sean Welsh (Sean)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, June 28, 2005 - 8:54 pm: | |
To answer your specific question:
No. Isolate ground and neutral at the panel.
In any given electrical system, ground and neutral should be bonded at exactly one place (or, put another way, one and only one place).
In the case of your genset, the bond is in the genset itself. So the two busses in the panel should be isolated.
The simple reason for this is that electricity will take as many paths as it can find. So if you have ground and neutral bonded at the panel, and also at the generator, then some of the return current will travel from the panel to the generator via the neutral, and the rest will travel via the ground. Since the ground is connected to the coach frame in both places, some of that current will travel in the frame, and you now have a "hot" frame, which is a shock hazard.
Also, the advice to use two separate breakers versus one two-pole breaker is suspect.
If you have the type of panel designed for 240-volt service (whether or not there are any 240-volt loads), then this panel must be fed by a two-pole breaker. Any condition which interrupts power to one leg of the panel must, by code and for safety reasons, interrupt both legs simultaneously.
HTH,
-Sean |
akrom
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, June 28, 2005 - 10:22 pm: | |
Hey Boy, I keep tellin you that legs is fer chikens and wimmen, and two PHASES are 240 volts, and they gotta trip at the same time on a two pole breAKER. Read Sean's post about 4 or 5 times, 'cuz he's a smart feller, and got his **** together. akrom |
Jtng
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, June 28, 2005 - 10:22 pm: | |
To clarify my comment (for Sean?):
Re:
"Genset panel has three 30 Amp breakers that feed three
separate 30 Amp female sockets (1 for front air conditioner, 1
for rear air conditioner, and 1 for coach 120 lights and
appliances). Front air conditioner and coach circuit feeds from
one 120 V lead from genset, rear air conditioner feeds from the
other 120 V lead from genset. "
And if you don't need 240v, I would suggest (as I had), to leave
it that way. If one circuit trips, you'll still have the rest powered.
(Most all older motorhomes were wired this way). |
Sean Welsh (Sean)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 29, 2005 - 1:11 am: | |
To clarify for JTNG, the breaker I am talking about is the existing two-pole breaker at the genset, per the original description. That can not legally or safely be changed to two single-pole breakers. It doesn't matter whether or not there is a "need" for 240 volts downstream of that.
And, Jimbo, I forgot to answer part of your question: Yes, if you are reading 240 between legs, then your genny is wired for 240. In order to change it to 120-only, more is involved than just the voltage regulator. Specifically, the way the windings are "strapped" needs to be changed. Also, the main breaker needs to change from a two-pole at X amps to a single pole at 2X amps. Consult your generator manufacturer for specific instructions.
If you are concerned about balanced loading of the generator, you might want to re-strap it for 120-only, which will evenly distribute the load on the windings. Bear in mind, though, that this has repercussions elsewhere in your distribution system, in terms of wire gauge and main breakers.
-Sean |
Richard Bowyer (Drivingmisslazy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 29, 2005 - 8:08 am: | |
To expound a little more on the subject. The existing voltage regulator will work fine if you decide to re-connect the alternator for 120 volt output only.
If it is a 12 lead alternator, you will loose approximately 1/3 of the rated output of the alternator when reconnectinf for 120 volts. If it is a 4 lead alternator, there will be no loss when connecting for 120 volt output only.
Typically, manufacturers DO NOT connect neutral to ground within the connection box itself. Generally this is done outsite the connection box. Be sure and check and make sure the neutral is grounded either inside the connection box or externally somewhere close to the alternator.
In my opinion, this connection should never be broken by any switching device of any kind. It is a permanent connection.
Richard |
Jtng
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 29, 2005 - 9:04 am: | |
From a 120/240 V Power Tech 10kw genset owner's manual:
The generator may be connected at the terminal board to deliver
120/240 volts to a 3 wire grounded neutral system, or 120-volts
only to a 2 wire distribution system. If any equipment requires
240-volts, then the 120/240-volt connection must be used. If all
equipment requires 120-volts then the 120-volt connection is
preferred, even if two lines leave the same switch box. The two
lines at the inputs to the switch box are both connected to the
un-grounded 120-volt lines from the generator. The 120-volt
connection enables the Electronic Voltage Regulator (EVR) to
hold the voltage very close to the 115 or 120 volts, as
initially adjusted, regardless of the power distribution amount
the different distribution lines. The 120-volt connection is
recommended if the entire electrical load requires only 115 or
120 volts.
Although the 120/240-volt connection may also be used when all
loads requires only 110 volts, it should be pointed out that
this connection, the 240-voIts, is regulated and the lightly
loaded phase, or line, will deliver a high line to neutral
voltage and the heavily loaded phase will deliver a low line to
neutral voltage. The heavily loaded line may have such a low
voltage that air conditioning will have more difficulty in
starting, and long starting lines may overload generator and
trip circuit breakers
http://www.acsi-us.com/support/manuals/Generator_Screen.pdf
(It contains schematics as well.) |
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