Connecting MEP to house

[JamAlRos]

I purchased a 50 foot RV power cord on Ebay for $180.00 and mounted a RV receptical to a 100 amp add-on panel that was on the outside of my house. The cable has 3, 6 gauge for 2 lines and a neutral, and an 8 gauge for grounding the unit through house ground. I keep the cord stored in a box on the trailer and just plug it in when needed. Works great and is only a couple of amps short of output, but since my house has not loaded the unit more than 60%, I think it will be ok.

 

[EO2NMCB]

I know this is a little old but I think that is important. There seems to still be a little confusion regarding grounding. Per OSHA's document liked to earlier, it says that you MUST connect it to a ground rod if connecting to the house. The only time you don't need to is when you are using appliances run only from a cord connected to the generator. However, a real ground (driven 8') is better than not having it regardless. The only places they don't necessarily like grounds are in high voltage substations because they are paths for very high fault currents to travel. Also, the neutral is not a ground even if it is grounded. When under a load, it carries current...

Big picture, keep it safe and ground that generator...

Whether the generator is portable of fixed-in-place, and whether its for life safety or optional standby, it must be grounded per the National Electrical Code (NEC). The NEC identifies that there are two methods of grounding:

• Connect a grounding electrode conductor from the genset to the ATS (automatic transfer switch), which is connected to the panelboard / main service grounding electrode conductor.
• Provide the genset with its own grounding electrode conductor.

Method #1 above is referred to as a Non-Separately Derived System and is defined by NEC 702.10(B). In this type of installation the equipment grounding (bonding) conductor must be bonded to the grounded electrode system, which is typically the main distribution panel/switchboard. Also, in this type of scenario, a 3-Pole ATS is required. Refer to the diagram below for further clarification:

 

[AndrewOH]

Whether the generator is portable of fixed-in-place, and whether its for life safety or optional standby, it must be grounded per the National Electrical Code (NEC).:

Although I agree with this in the interest of safety, I am not sure I agree that the NEC requires this.
I read through the NEC 2008 edition and found this:

250.34 Portable and Vehicle-Mounted Generators.
(A) Portable Generators. The frame of a portable genera-
tor shall not be required to be connected to a grounding
electrode as defined in 250.52 for a system supplied by the
generator under the following conditions:
(1) The generator supplies only equipment mounted on the
generator, cord-and-plug-connected equipment through
receptacles mounted on the generator, or both, and
(2) The normally non–current-carrying metal parts of equip-
ment and the equipment grounding conductor terminals of
the receptacles are connected to the generator frame.

That being said, I will still always ground my generator...

 

[212sparky]

Ground the frame of your generators to a local ground rod. Use a 4 conductor cable (2 hot, 1 neutral and a ground) that ground in the cable is tied between your gen set and structures grounding system. Your bonding takes place at your main panel since your neutral is not switched in the transfer switch. Remember if you have a sub panel you are using as an emergency panel you still need a was to interlock the breaker from your main distribution panel to your sub panel. LOTO ( Lock Out Tag Out) will work so it can not be accidentally closed, back feeding the system. PM me if you have any questions

 

[n1oty]

Although I agree with this in the interest of safety, I am not sure I agree that the NEC requires this.
I read through the NEC 2008 edition and found this:

250.34 Portable and Vehicle-Mounted Generators.
(A) Portable Generators. The frame of a portable genera-
tor shall not be required to be connected to a grounding
electrode as defined in 250.52 for a system supplied by the
generator under the following conditions:
(1) The generator supplies only equipment mounted on the
generator, cord-and-plug-connected equipment through
receptacles mounted on the generator, or both, and
(2) The normally non–current-carrying metal parts of equip-
ment and the equipment grounding conductor terminals of
the receptacles are connected to the generator frame.

That being said, I will still always ground my generator...

I hope you realize that Article 250 covers general grounding and bonding only and can be (and is) modified by more specific NEC Articles. I suggest you go back to your code book and read 702.1, then come back here and report your findings. If you want to operate your generator as a portable and NOT connect it to premises wiring, your point about 250.34 applies. The MOMENT you connect to premises wiring, Article 702 serves to modify Article 250.

John

 

[AndrewOH]

I hope you realize that Article 250 covers general grounding and bonding only and can be (and is) modified by more specific NEC Articles. I suggest you go back to your code book and read 702.1, then come back here and report your findings. If you want to operate your generator as a portable and NOT connect it to premises wiring, your point about 250.34 applies. The MOMENT you connect to premises wiring, Article 702 serves to modify Article 250.

John

I agree and that is what I said earlier on. If you want to use a generator such as on a job site for a drill, it doesn't require you to pound in a ground rod. Even with that said, I will never operate a generator without a grounding rod, ever... I've been shocked before from fautly wiring and it is something I will try to never repeat again.

 

[n1oty]

I agree and that is what I said earlier on. If you want to use a generator such as on a job site for a drill, it doesn't require you to pound in a ground rod. Even with that said, I will never operate a generator without a grounding rod, ever... I've been shocked before from fautly wiring and it is something I will try to never repeat again.

My error. I apologize. I completely missed your post from 8/22 where you mention that point.

John

 

[dependable]

Is there any substantial advantage of a manual transfer switch over a lock out plate like the 'Interlockkit' ? The lockout plates look like a good, simple solution.

 

[AndrewOH]

Is there any substantial advantage of a manual transfer switch over a lock out plate like the 'Interlockkit' ? The lockout plates look like a good, simple solution.

I'm in the same vote myself and am curious about any replies regarding this. I have so far decided to put in a manual transfer switch due to what I've seen of the interlock kits for the circuit breakers. It just doesn't seem that well built to me. But, that being said, as long as your circuit breaker doesn't break, it should work just fine... With that setup, I would personally use a service disconnect switch prior to the panel just as added safety (plus, if you have to work on your panel yourself, it is always nice to do so with a completely dead panel).

-Andrew

 

[Speddmon]

I made my own interlock plate, and I like it just fine. It is heavier duty than the ones you buy, and very solid. They work good for what they do. It's not like you're going to be using it daily, your breakers are not rated to be used as switches anyway (They make special breakers that are to be used as switches for commercial/industrial applications).

As far as working on the panel goes...I've grown acustomed to working on live equipment/panel boards. In a lot of industrial maintenance applications, you don't have the privilege of shutting off an entire panel and a good portion of a plant or production line to work on it...so you do it hot.

 

[islandguydon]

The only input I have it to always install a manual transfer switch. When it comes to utility power you are dealing with death or a disaster if the system is not installed properly. Also ground the MEP with at least 1 ground rod and check the acorn nut for corrosion on the home ground rod supplied by the utility.

 

[Speddmon]

The only input I have it to always install a manual transfer switch. When it comes to utility power you are dealing with death or a disaster if the system is not installed properly. Also ground the MEP with at least 1 ground rod and check the acorn nut for corrosion on the home ground rod supplied by the utility.

You do not always have to install a transfer switch. The interlock kits are an approved means of disconnect for generator installations and are widely used. They are UL approved, and safe to use and install. It is up to the individual whether they want to use one or go for a full blown transfer switch.

I do agree with you about grounding the set and inspecting the homes grounding conductor occationally though.

 

[islandguydon]

I was thinking of back feed to protect the line workers and SAFETY FIRST. I do agree with the interlock system. I just went a different direction.

 

[quickfarms]

If you understand electricity the transfer switch and interlock perform the same function. The existing panel is what determines which one is used. You can also use a lock out device, that is an electrician will probably hook up a generator in an emergency.

 

[Wildchild467]

Thanks a lot guys for all the good information you are posting here. Someday I would like to set up my house so I can run my MEP-002A to power the house during a power outage. I have a good friend who is a licensed electrician and will have him hook up what I need to power the house. I like learning new things and working with him will be a good experience. I am more of a mechanical guy as far as working on things and have not had much experience in the AC voltage stuff. I have a 100 amp service by the way.

 

[Isaac-1]

Regarding transfer switches vs interlock kits while both are legal in most areas it comes down to one detail:

Interlock kits make sure the breaker switches are in "safe" positions before switching power sources, but do nothing to make sure the contacts are in a safe position. In other words it is possible a breaker will be "off" but the contacts have welded themselves closed giving a false sense of security.

A real transfer switch will have some type of physical mechanism (knife switch, big rocker switch, etc.) that prevents the possibility of both sources being connected at once.

Ike

p.s. Yes breakers do fail in the welded closed position, it just happened last month at my elderly mother's house, she had a handy man changing out a light fixture and switch, and he could not find the breaker to turn off the power to the fixture even after turning off all the individual breakers in the box, however it did go out when he turned off the main breaker in the panel.

 

[AN/ARC186]

I've installed quite a few of the following types of generator input devices, In my opinion(and it's just that, my opinion)each has it's own pros-cons.

Transfer panel- sometimes mistakenly called a transfer switch, has 2 position switches for each circuit as well as a circuit breaker. allows for selection of line or genset power.
Pros-1) peak load can be offset by using generator instead of line power.
2) already connected, easy to transfer over
Cons-1) power transfer limited to number of circuits connected to panel, doesn't allow for flexibility easily.
2) Usually pretty expensive, breakers and switches not always of the best quality

Generator Safety Interlock- Mechanical linkage that will not allow for simultaneous operation of line and generator power.
Pros-1) Inexpensive
2) Easy to operate
Cons-1) Generator can easily be overloaded if the load is not adjusted at the panel, such as turning off unneeded/ high draw breakers.

Transfer Switch- sometimes called an A/B switch.
Pros- 1) can be purchased in manual or automatic configuration
2) Usually of high quality
3) most auto types will start and perform maintenance runs on genset.
Cons-1) Generator can easily be overloaded if the load is not adjusted at the panel, such as turning off unneeded/ high draw breakers.
2) Usually expensive, even for manual switch.

I've installed a manual 400A transfer switch for my house. it's a simple and reliable.
I've also color coded my circuit breakers for generator operation so even if I'm not home my much better half can do the switchover.

 

[Isaac-1]

You left out the simplest one, just use extension cords

 

[panic_button]

My choice was a new a Square D 40-Circuit 20-Space 200-Amp All-in-One/Combination Main Breaker Load Center Value Pack (http://www.lowes.com/pd_286869-296-...tId=3366856&Ntt=square+d&Ns=p_product_price|1), $200 @ Lowes, less than that with the 10% military discount. It comes with the $70 interlock already installed. The only thing I changed was replacing the 30A generator breaker with a 90A. Color coded the breakers that I don't need during an outage so the wife knows, 3 hours total to install. Cheaper than a manual transfer switch, and it works like a champ.

PS I do have a 200A Generac NEMA3 Auto switch I could get rid of, due to the county wanting me to install a 40KW generator to use it...

 

[AndrewOH]

My error. I apologize. I completely missed your post from 8/22 where you mention that point.

John

I appreciate you double checking my posts. This is all new to me and I can't afford to have a professional do this for me. I've been researching like a fiend trying to make sure I do everything correctly. I've already learned so much from this site, it's incredible...