Hooking Generator to Residential Load Center

Status
Not open for further replies.
aelectricalman

aelectricalman

Senior Member
Location
KY
Customer wants to have "capabilities" to hook generator to line side of Electric Panel (enabling her to switch only the breakers she wants (In case of power failure). She wants to know if there is a certain type of panel she would rather have installed (new construction) so that this is done with ease. Is there a conversion kit to be purchased? Is this commonplace? I've just never ran across this in my youthful days of contracting. For those of you that spend your time answering questions, I can not thank you enough. I enjoy this forum and like to contribute any way possible. Thanks,

ACE
 
Re: Hooking Generator to Residential Load Center

SQ D makes a QO panel that has a manual transfer switch built in it is a 4/8 circuit.inexpensive around $68.00 + breakers.We usually rough in lighting,micro,fridge circuits to it.Generator side gets a male twist lock cord cap .Power goes out H/O fires up the genset plugs in flips one switch done very cheap to install and great profit maker.
 
Re: Hooking Generator to Residential Load Center

Had an idea here... Just scroll past the yelling.

This is $220, allenwayne's idea seems more affordable.
163249_4.jpg
 
Re: Hooking Generator to Residential Load Center

Be careful where you connect the transfer switch!!!
If connected to the line side of the service, the transfer switch must be labled as "Suitable for Use as Service Equipment". The switch, if part of the service, must also be capable of switching whatever loads are available downstream, underload. Not a problem with a current limiting, small generator but could cause some excitement when the utilty comes back up.
The final-and most potentially lethal- problem with making the connection on the line side is your generator is capable of back feeding the utility. There has to be a way to isolate from the utilty when you get into the power generation business. Your little 3KW 120/240V generator could be feeding a 50KV suprise to someone working across town.
It would be better to have a way to pickup the loads after the service disconnect.
 
Re: Hooking Generator to Residential Load Center

Rick, Transfer switches make it Impossible to back feed the utility lines. That's one reason they are the correct way to do it! But, you're right, if you are feeding the ENTIRE panel with a transfer switch it must be listed for Service Use.

Dave
 
Re: Hooking Generator to Residential Load Center

Dave,
I wanted to make sure that someone connecting a backup power supply common to a utility supply was aware of the sometimes unseen dangers of paralleing a second supply. A service rated transfer switch is very expensive and may not be justified for emergency residential loads.
You are correct that a properly installed transfer switch is the right way to do this. However, I have witnessed numerous installations, where the bus connection is made by way of a panel mounted branch circuit breaker, back fed from a small generator output. If the main is not opened prior to the generator starting, the utility is back fed also.
Not permitted by code, that's for sure, but done just the same more times than you'd think because of the unfamiliarity with transitional power systems in the residential field.
I just want the electrician to be careful where and how he connects a second power source.
 
Re: Hooking Generator to Residential Load Center

I understand, but you said Transfer Switch! An installation like you mentioned is NOT a transfer switch.

Dave
 
Re: Hooking Generator to Residential Load Center

Actually, I was only expanding on what someone else said recommending transfer switches....

What caught my atention was making connection on the line side of a panel and selecting the loads, presumably from all loads available. I take that as a potential parallel connection.

For the record:
1. Have the customer identify the critical loads that they might want supplied in an emergency now. That can get out of hand in a hurry if EVERYTHING is important. A plug in the kitchen, a few lights and don't forget the TV are really all that you need. More is good but, not economical. Make them choose.
2. Supply those loads from a separate sub-panel, fed from the main service. It can be right next to the service or wherever.
3. In the future, select a transfer switch and generator that meets the ratings of whatever those loads are determined to be critical.
4. Feed the transfer switch with the sub feed OCPD and the generator output OCPD; the load side goes to the sub panel.
5. Make sure your transfer switch is capable of switching the neutral- that back-feed thing again that has me in an uproar!
6. Make sure the generator itself is grounded properly. Bonded to the grounding electrode conductor will save a bunch of grief and keep ground loops away.
7. There are other ways to do this, equally safe but....I'm the one designing this system!

THERE!
;-))
later
 
Re: Hooking Generator to Residential Load Center

Make sure the generator itself is grounded properly. Bonded to the grounding electrode conductor will save a bunch of grief and keep ground loops away.
Click to expand...
Rick, Can you describe what you mean by "grounded properly", when the transfer switch opens the neutral, as you specified?

What would you connect to the grounding electrode conductor, the generator winding, the generator frame, or both.
And, would you run three wires or four wires between the generator and transfer switch?

Ed

[ January 28, 2005, 03:23 PM: Message edited by: Ed MacLaren ]
 
Re: Hooking Generator to Residential Load Center

I KNEW this would happen! You guys don't let anything get past you!

Ed,
I can tell you what wiring scheme and what properly grounded is as soon as a generator is defined. 2 wire, 3 wire, single phase, three phase, fixed, portable, nuclear....whatever it is, will dictate most of your answers.
For the sake of keeping things simple- ground according to manufactures instructions will do.

I presumed that the generator would be portable rather than stationary, single phase 120/240V, under 5kW, in our example. For the sake of answering your question, we will continue in that presumption. MOST commercial manufactures of home use portable generators already have a center tap bonded to the case of the generator, there is a main disconnect to a receptacle that supplies output. A grounding point is also typically furnished and it is here that the generator will be "properly grounded" to a suitable ground reference. Since the loads in the dwelling can be served from two supplies simultaneously (those deemed critical and those not) and can also have interconnection between the two power systems -through touch, shielding of low voltage cables, etc.- there is a need to bond the two electrical systems together. Since we are already having to "properly ground" the generator, it is best to also reference the existing building ground when grounding the generator so the two systems remain at the same potential.
When the transfer switch is put between the service-normal or emergency- and sub panel, both the transfer switch and sub panel must have neutral/ground separation.
If the neutral were solid, the ground reference would be at both the service entrance and at the generator. In my suggestion, the way to avoid the ground loop problems, tricky grounding and bonding is to keep the "separate" in "separately". Disconnect from one system, connect to the next using the same ground reference for both.
Not a huge concern; I guess you could use the equipment grounding conductor at the transfer switch to ground your generator and NOT switch the neutral. In my world (healthcare) solid neutral transfer switches cause a lot of power quality problems. I like the separation of this neutral here and that neutral there to keep stray voltages away. But that is a personal preference.
 
Re: Hooking Generator to Residential Load Center

I wired a home recently using Square D breaker interlock device for generator hook up.Do not have model # on hand,but the way I wired it was:used a gen tran 30 amp 4 wire male connection outside,tied to a 30 amp breaker in panel.Interlock prevents main and 30 amp breaker from being energized at same time.Found a lot cheaper and easier to use than a gen tran panel,and all breakers can be utilized[of course I will inform customer of load limitations]anyone else ever use this before?
 
Re: Hooking Generator to Residential Load Center

I KNEW this would happen! You guys don't let anything get past you!
Click to expand...
Yep, put a bunch of electricans together and Look Out! One of them will say Something that the others will question or completely disagree with. It's a very "Passionate" trade I must say! What other trades sit around talking about work so much?!?

Note to self: Next time I have a question about transfer switches...see Rick's post! :)

Dave
 
Re: Hooking Generator to Residential Load Center

If the neutral were solid, the ground reference would be at both the service entrance and at the generator.
Click to expand...
This is the only part of Rick's description that might require clarification.

If the neutral were solid (unswitched in the transfer switch), the unit is not deemed to be a separately derived system (SDS), and the neutral should not be re-grounded at the generator, and should not be bonded to the generator frame. (Diagram 1)

Ed

Gen4.gif


Gen5.gif


[ January 29, 2005, 07:58 AM: Message edited by: Ed MacLaren ]
 
Re: Hooking Generator to Residential Load Center

..so when wiring a transfere switch for a customer, what do I need to look for. I've not wired one before, so treat me like im a 12 year old. Do I need to know whether its a 3 wire or a 2 wire generator? Thank you for any help guys.
 
Re: Hooking Generator to Residential Load Center

when wiring a transfer switch for a customer, what do I need to look for.
Click to expand...
The generator and transfer switch must be "compatible" in order to be code compliant.

In other words, if the generator manufacturer has bonded the winding center tap (neutral) to the generator frame, the transfer switch must open the neutral conductor. (Diagram 2 above)

Most portable generators, that were intended to supply cord-connected loads through receptacles mounted on the generator, will have the neutral-to-frame bonding connection.

Generators that were intended to be connected to a premise wiring system through a transfer switch may not have the neutral-to-frame bonding connection.
If it does not, a solid-neutral transfer switch (one that does not break the neutral) should be used. (Diagram 1)
Do I need to know whether its a 3 wire or a 2 wire generator?
Click to expand...
Not sure what you mean. I don't think you will see many single voltage, single phase generators.

Ed
 
Re: Hooking Generator to Residential Load Center

Pardon me if I am wrong but off the top of my head wouldn`t a generator that has a 120/240 4 wire twist lock receptacle not have a bonded neutral otherwise why have a 4 wire connection?
 
Re: Hooking Generator to Residential Load Center

The wiring/cord between a 120/240 volt single-phase generator and it's transfer switch is required to have four conductors whether the generator neutral is bonded to the frame or not.

See my diagrams above. (Page 1)

Ed
 
Status
Not open for further replies.
Top