transfer switch for a portable generator

keastAugust 22, 2008

I've got a question as to what type of switch to use for a portable generator hook up for residential use. I have a 7500 watt portable generator with a 12125watt surge capacity. In a previous home I had it hooked up to the main Square D panel with one of those lock out breakers made for the panel. I know some here don't like them but they are approved for code. So now I'm in a new house and no Squared D main and I want to legally hook up the genset. I'm not a big fan of the transfer switches with the set number of circuits that run off them (6-10). I'd prefer one of the switches that hooks into the main drop before the panel that allows the whole panel to be run from the genset. This way I can pick and choose which circuits I choose to power. One I had in mind is this one

I have a 200 amp service. I know I'd have to moniter what I am running so I wouldn't overload the generator and fry it. This way I could shut things down and heat up the hot water heater as needed or use other larger loads. My question is there any advantage or disadvantage of this type of switch vs the other self contained transfer switches? Also from the sparkys, It seems that the single switch would be less expensive to install since you wouldn't be hooking up all the sub circuits to it. Can anyone give me a ball park figure on what I'd pay to have it installed. I'd probably do the generator inlet run my self and have the wire there for the electrician to install. I already have the inlet box for outdoors hook up to the generator. Lastly, can anyone comment on why they don't like those lockout breakers that go in the Square D panels.

In advance, thanks for the great advice that you folks have always responded with over the years. You've saved me from doing some stupid things a few times.

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Unless you already have a separate service disconnect from your panel, to use this switch as you want it would need to be the "Suitable for Use as Service Entrance Equipment" version.
It would be installed before your main panel.
Your main panel would be converted to a sub a panel. All the grounds and neutrals would need to be separateted.
You would need the POCO to shut off your power so the service could be be reconfigured.
This is a major service change. Not likely DIY work.

    Bookmark   August 22, 2008 at 8:19AM
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Joed, thanks for your response, I realize that I wouldn't be doing it my self. I'd probably consider doing a regular transfer switch with the separate circuits and having that inspected. I've put in a number of circuits, including a 220V spa that passed inspection, but my talents end there, I wouldn't fool with anything where I have to coordinate with POCO and the main line though. Just wondering about adavantages vs disadvantages, also an idea of expense of one install vs the other by an electrician. For a regular transfer switch I figure you'd still get a lot of time in by the electrician since he'd have to move 6-10 circuits into the transfer box even though he wouldn't have to deal with the POCO coordination to shut down power. Price difference between the two types of switches aren't that much and I'd prefer to have the option of choosing which circuits I'd like to put in service when needed.

    Bookmark   August 22, 2008 at 1:30PM
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Since you are going with a manual setup, the two pole transfer switch that would give you use of the entire panel is the only way to go.
Most manufacturers have generator imterlock kits for their loadcenters so you should look into this before you spend the time and money to install a seperate transfer switch.
What type of loadcenter do you have in your house?
What is the setup of the service?

    Bookmark   August 25, 2008 at 11:23PM
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keast, "coordinate with the POCO" doesn't mean anything beyond your talents - it just means you need to call them and have them turn off the power before you do your work, and turn it back on after. :)

    Bookmark   August 26, 2008 at 10:09AM
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If that is what you wish to do, you need a 3-pole transfer switch (TPDT), not 2-pole
The neutral needs to be disconnected (for line safety) and transferred also.

    Bookmark   August 26, 2008 at 10:18AM
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"keast, "coordinate with the POCO" doesn't mean anything beyond your talents - it just means you need to call them and have them turn off the power before you do your work, and turn it back on after."

No reason to have the POCO shut off power.
Turn off all circuits, turn off the main breaker, pull the meter.

    Bookmark   August 26, 2008 at 7:12PM
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Sorry ZL700 but in this case you do not want to set up a seperately derived system by switching the neutral.
All that is required is a two pole switch.

I don't know where you live but in every locale that I have ever worked, it is illegal to pull a POCO meter unless you are a licensed master electrician and that does not apply everywhere.
Not only that, but it is dangerous to do so unless you know what you are doing and take the necessary precautions such as PPE when pulling a meter.
There have been a rash of documented incidents in the past year in which parts have failed when old meters were pulled producing a flash that caused serious injury.
Call POCO and be safe.

    Bookmark   August 26, 2008 at 8:17PM
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Dezwitt, you a licensed master electrician?

All generators should be labeled as either floating neutral or bonded neutral. The majority which I have seen is not labeled, and from my research are most likely neutral and ground bonded to the chassis. Using an ohmmeter to measure resistance between neutral and ground will confirm either way. Make sure the generator is not running while checking. Either way will work for home use, but the transfer panel must be wired differently in each case.

For a generator with bonded neutral, the transfer panel MUST be three poles and switch neutral for all circuits. The single connection point for neutral and ground will be in the generator. The ground wire will come back along the same cord and bond to the household ground.

For a generator with floating neutral, the transfer panel can be either two or three pole, but only TWO poles will be used. Neutral is not switched, and the connection point remains in the main service entrance panel. This is how my home has been wired. My transfer panel has three poles, but only two are used.

Using a generator with bonded neutral and ground in a system which does not switch neutral in the main panel leads to a potential safety issue. Neutral and ground will be connected at both ends of the extension cord, thus making them one conductor. As wire has a certain finite resistance, a voltage will develop when current flows through. This voltage will appear at the chassis and want to find a path to ground. Touch the chassis and you will be providing such a path. Normally this voltage is very low, but if there are problems elsewhere, it could become dangerously high. Safe operation can no longer be assured. Wired properly the neutral wire would be isolated at one end, preventing ground wire current and ensuring the chassis remained at zero volts.

Not knowing what is being connected or how it is used is why I suggest 3-pole.

    Bookmark   August 27, 2008 at 9:54AM
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The 5-10 KW portables that I have looked at recently have been marked "Floating Neutral". This is the wrong way for a portable unit. It should provide the single neutral-to-ground bond. There appears to be no factory provision for easily changing it. I added a bonding strap and re-labeled my unit. Probably violates the warranty, but looks to me like it makes it NEC legal.

I hope the bigger ones make it easier to pick the right way.

    Bookmark   August 27, 2008 at 1:20PM
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"For a generator with bonded neutral, the transfer panel MUST be three poles and switch neutral for all circuits..."

While I'm well aware of what the NEC says, it is worth pointing out that there are probably thousands of older installations where 2 pole switches are used with "bonded neutral" gen-sets. I have a Dayton standby genset that came from the maker with with a bonded neutral and a two pole transfer contactor. The whole bonded vs floating neutral, switch the neutral or not thing is a relatively new issue. IMHO, any transfer switch is preferable to the usual alternative (backfeeding via a 240V outlet and cheater cord) by a significant margin.

    Bookmark   August 27, 2008 at 1:51PM
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whoa! looks like I opened up a can of worms. Well don't worry about me pulling the meter, I'd pee my pants in the process that would add to the danger of such an act. Thanks for all of the discussions. I thought only square D had a lock out switch for their main panels and wasn't aware a lot of other companies did also. Mine is a GE 200 amp top feed. I've found a company that makes main breaker inter lock switches for many types of panels and will likely use one of them and save a lot of time, hassle, and money in the process. This will give me the desired benifit of being able to pick and choose circuits as needed only.

My reasearch has lead me to more questions than answers though. I understand that the lock out switches, and most residential transfer switch panels allow the neutral and ground going back to POCO lines. Yet this situations is one of the many arguments against back feeding a breaker or the dryer outlet. Dispite that argument, these units are code approved for residential use. At least there is not the possibillity of having the main breaker on when using the genset with these devises. I guess there could be a rare situation where the main breaker is faulty or corroded enough to allow feed back into the line in the off position.

The last posts dicussing floating neutrals in generators has me preplexed also. I ran across a site from a Canadian Electrician dedicated to this issue. He is advocating that you must use a floating neutral in all generators feeding a transfer switch system and actually has directions on how to accomplish this on many models of generators. According to him, most generators ship as bonded neutral models and should not be used that way for feeding a transfer switch or you risk getting shocked incertain open neutral situations, however remote they may be. I could post the web site if anyone would like. The thing the puzzles me is that there are lot of manufacturers of generators and transfer switches and none seem to address these isssues, if indeed they are valid, but they seem to be being installed by electricians and are code approved. Also, the POCO's are well aware that this is being done and not advising against it. Infact some POCO's offer service to sell, install such equipment and to maintain it. I'm sure this will stirr up a few more posts.

Thanks for all the great info I gather from this site, sorry for the long post. There's another storm out there in the Atlantic, I need to get this done.


    Bookmark   August 27, 2008 at 5:49PM
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As the poster of the 3 pole switch requirement, I agree there are plenty out there wrong. But if it was me I wouldn't want the lineman knocking on my door that just took a jolt.
I remember once the electric company being sued once by a homeowner that claims someone removed his oil plug on his generator after an ice storm, causing his gen to seize.

Did it vibrate loose or what?

Turns out he plugged it into a outlet and was charging the lines leaving his house


    Bookmark   August 27, 2008 at 6:46PM
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I think we can summarize it as:
-Backfeeding without a lockout or transfer switch is terribly dangerous, and illegal. Approved lockouts are not risky.
-Whatever configuration you have, you should have exactly one point in your wiring where the neutral and ground are bonded, no more and no less.
-The single point bond can be achieved with a 3-pole transfer switch and a bond at the generator
-With a 2-pole transfer switch the bond must be that one already in your main panel or other first service equipment. Obviously, the generator must have floating neutral in this setup.
-There is very little risk associated with a properly wired 2-pole transfer switch system

    Bookmark   August 27, 2008 at 6:59PM
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I've only found one company that makes an interlock switch for my GE inlet panel. It's $149 for a piece of stainless and some screws. Does anyone have other sources for for such a product. Sure would be nice to have a square D panel where they make the interlock and it's a $55 piece of stainless. It's still cheaper and easier than the tranfer panel and accomplishes what I want.

    Bookmark   August 27, 2008 at 10:34PM
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Find an electrical supply house that sells GE products.
They will have the interlock kit for considerably less money.
I don't know where you live but in Florida, the big box stores carry some of the interlock kits.
I just bought one for a GE loadcenter and paid about $59 for it.
You will need to give them the model number of your panel.
You will also need a subfeed breaker.

    Bookmark   August 28, 2008 at 7:31PM
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