Generator wire, conduit and house penetration question


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Old 09-20-13, 12:41 PM
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Generator wire, conduit and house penetration question

My daughter and family (including mom-in-law) just moved up here (Rhode Island) from Texas, bought a house and moved in. So far so good, but there's a new reality dawning now that they consider their water is pumped in from a well, that it gets real cold here in winter, and that there will almost certainly be occasional power outages. This combined with the fact that they travel, leaving mom who is barely mobile, alone for as much as a week, makes a backup generator neccesary for peace of mind if for no other reason.

With that prelude I’ll cut to the chase:

14kw Kohler generator to be sited 25’ from house with 4 day propane supply.
Transfer switch (14 or 16 circuits, not sure which) mounted inside next to main box.

Specs state that the unit has a 70 amp breaker. I think I’ll have to use #6 THWN wire but would be happier with #8 if code permitted.

I Plan to trench and bury the wire in flexible conduit. What conduit size is adequate for three wires (#6 THWN)? Need to also bring over control wires plus 120V power for battery and heaters – my guess is that will require a separate conduit – any thoughts on that?

I’ve wired up a transfer switch before so feel OK doing it myself. A local inspector will check the project from beginning to end.

My agita is the penetration into the house through clapboard siding, having never done that before. I know it should be straightforward, but I’ve screwed up “straightforward” jobs in the past and I don’t want to butcher this one. I don’t even know what fittings to ask for at the electrical supply! I’ll just throw myself on their mercy and hope they treat me like family.

Any thoughts will be appreciated.
 
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Old 09-20-13, 01:33 PM
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14kw Kohler generator to be sited 25’ from house with 4 day propane supply.
Transfer switch (14 or 16 circuits, not sure which) mounted inside next to main box.

Specs state that the unit has a 70 amp breaker. I think I’ll have to use #6 THWN wire but would be happier with #8 if code permitted.
14 kw is 58 amperes at 240 volts. You need #6 copper conductors at a minimum. If that 14 kw is continuous load and there is a higher peak load figure you might want to consider going to #4 copper conductors. I would also check history of the area for power outages to see if a four day fuel supply would be sufficient.

Are you considering a transfer PANEL?


I Plan to trench and bury the wire in flexible conduit. What conduit size is adequate for three wires (#6 THWN)? Need to also bring over control wires plus 120V power for battery and heaters – my guess is that will require a separate conduit – any thoughts on that?
Why would you want to use flexible conduit? Schedule 40 PVC where buried and transition to schedule 80 where it comes above ground is both better and less expensive. Minimum size for four #6 is 1-inch; for four #4 use 1-1/4 inch minimum. The control wires need to be in a separate conduit. The 120 volt for the heater and battery charger MAY be allowed in the same conduit as the control but it is best to have it in a third conduit, you have to follow the manufacturer's instructions.


My agita is the penetration into the house through clapboard siding, having never done that before. I know it should be straightforward, but I’ve screwed up “straightforward” jobs in the past and I don’t want to butcher this one. I don’t even know what fittings to ask for at the electrical supply! I’ll just throw myself on their mercy and hope they treat me like family.
Simply use the appropriately sized (conduit size) LB fittings.
 
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Old 09-20-13, 06:15 PM
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This combined with the fact that they travel, leaving mom who is barely mobile, alone for as much as a week, makes a backup generator neccesary for peace of mind if for no other reason.
Obviously, you must be planning on an automatic transfer switch/panel. Have you thought out the circuits to go in the transfer panel and have you calculated the load, is 14 KW big enough? I agree with Furd, a 4 day propane supply may not be enough. You need to look into the outage history for the area.
 
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Old 09-21-13, 06:15 AM
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A smaller generator would give you more run time. I run a 7 Kw auto generator and it has no problems running the well pump and all lights and outlets. But I do not have AC, heat pump, stove or dryer wired to my transfer switch.
 
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Old 09-21-13, 07:52 AM
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Thanks for responding.

The peak continuous load is unlikely to exceed 7 kw so 14 kw will provide a 100% margin. Peak transient load may come from the well pump but I haven’t checked that out yet.

Furd, you mention four wires in the power bundle. I plan to drive a ground rod next to the generator and thought that I would need to run just three wires into the house. Appreciate your advice re PVC vs. flexible conduit.

The local Propane supplier suggests a four day supply based on their ability to refuel in that span if necessary. As it is, there will be two 120 gal tanks next to the unit.

Yes there will be a transfer switch and a panel of selected circuits.
 
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Old 09-21-13, 08:02 AM
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You normally don't connect the generator to a ground rod. In any event the ground rod is only for a GEC (Grounding Electrode Conductor) which handles atmospheric electrical charge buildup. The fourth wire (if used*) is the EGC (Equipment Grounding Conductor) that provides a low resistance path to clear faults (shorts) by tripping the OCPD (breaker or fuse). GEC is often not a low resistance path and can not substitute for an EGC.

*Note in the case of a generator you shouldn't use an EGC if the neutral and ground are connected at the generator.
 
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Old 09-21-13, 08:40 AM
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Have you talked to a Kohler dealer? I'm sure they can answer your questions (along with an installation manual that should come with the unit). The warranty on the Kohler unit requires that a dealer be used for installation and startup for the labor portion of the warranty to be valid. You can probably bargain for some DIY labor in the installation to help with cost.

Generac does not require dealer installation for full use of their new 5 year warranty. Their 14kw unit comes with a connection box with how to instructions to mount at the entry point when used with the packaged 14 circuit switch. Code may also require a disconnect if the generator is located at a distance from entry.

Look into the warranty issue if you want to go with Kohler.

BTW, I think you still need all 4 wires to the house, plus control wires. Grounds all need to be connected. Control wires can be in the same conduit if insulation rated at the same voltage and the manufacturers instructions permit. You really need to comply with both installation instructions from the manufacturer as well as electrical codes. You need to discuss all this with a qualified electrician.
 
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Old 09-21-13, 12:06 PM
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My 7 Kw Generac system came with an 8 circuit auto transfer switch and instructions for installation. It did require 4 wire power since it is not bonded to neutral. It also said to use a ground rod at the generator. LP consumption is 0.82 gal/hour at half load and 1.47 gal/hour at full load.
 
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Old 09-21-13, 03:04 PM
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A ground rod at the generator isn't a NEC requirement, but some inspectors want to see one there.
 
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Old 09-22-13, 07:40 AM
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Part of code compliance is following manufacturers installation requirements for listed equipment.
 
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Old 09-22-13, 08:16 AM
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My Generac had "INSTALLATION GUIDLINES". Even the guidelines can be vague.

exp.
Connect an approved grounding conductor to the grounding electrode terminal on the corner support and to an approved earth ground or grounding rod as specified by local regulations.

So it's your guess as to what the inspector will or will not call a manufacture requirement.
 
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Old 09-22-13, 09:11 AM
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Right. That depends on what part of the sentence "as specified" refers to, likely the "or" just preceding it. "Connect" is a command as opposed to "If required by local regulations, connect...". The English language can easily be subject to various interpretations. A comma after the word support would make it clear if it were meant to be a requirement.
 
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Old 09-22-13, 11:50 AM
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exp.
Connect an approved grounding conductor to the grounding electrode terminal on the corner support and to an approved earth ground or grounding rod as specified by local regulations.
That tells me a ground rod isn't required unless the inspector wants to see one.
 
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Old 10-05-13, 05:18 PM
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Thanks for all the help

Thanks for all your responses. They've really been helpful.

Here's where I (think) I am at this point.

- 14 kw Kohler RESA
- 200 Amp transfer switch (going with whole house service, it's what they want and it beats rewiring 16 circuits into a panel).
- Will pound in ground rod. If nothing else it will ease tension.

Still have some details to nail down:
- Use end lugs to connect #6 stranded wire? Have to buy special crimping tool that I'll probably never use again?
- Generator sited 45 feet from house - Require external disconnect? - will check with inspector. Anyone run into this?

Just sat down and listed all the stuff I need for this job and undoubtedly missed some. Intimidating.

power wire – AWG #6 – THWN-2 --- 2 black, 1 white, 1 Green (60’ each)
control wire – AWG # 14 or #12, need 150 – 250 feet (divided into 4 lengths) depends on Kohler supplied control wires – get colors to match Kohler’s colors if available
Power wire for battery/heater - THWN-2 AWG # 12 - at least 60’, maybe double
PVC (Sched. 40) pipe for power and for control (buried in trench) plus connectors
Probably five 10’ lengths each (1¼ inch for power, ½ inch for control)
PVC (Sched 80) pipe/adapters/connectors to bring wires out of trench
PVC pipe cement
Large/small flexible conduit for final run to Gen., into house and to transfer switch – about 15’ each
adapters to connect flexible conduit to Sched 80 pipe
fittings to penetrate generator housing
fittings to penetrate house
ground rod/strap/connector
wire stripper for AWG #6 stranded wire
may need end lugs for wire. If yes, need 4-8 lugs and crimping tool
200 Amp Service Cable – to go from transfer switch to main box – 10’ ?
Penetration fittings for transfer switch – supplied by Kohler???
Caution tape - required by inspector to inspect open 18" trench!

Thanks again guys.
 
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Old 10-05-13, 06:01 PM
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A trick for installing a ground rod is to just fill a small hole with water and lift and drop the rod in that water. It worked great for me (8 foot rod). Also my control wires only needed to be 20 AWG but I used 16 AWG. Are you mounting your starter battery inside the house? Mine is mounted in the generator housing.
 
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Old 10-05-13, 06:38 PM
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Still have some details to nail down:
- Use end lugs to connect #6 stranded wire? Have to buy special crimping tool that I'll probably never use again?
If the lugs on your generator and transfer panel aren't sized to accept 6AWG conductors, something's wrong. You should only need a sharp knife and an allen wrench or screwdriver at each end.
- Generator sited 45 feet from house - Require external disconnect? - will check with inspector. Anyone run into this?
Check

Just sat down and listed all the stuff I need for this job and undoubtedly missed some. Intimidating.

power wire – AWG #6 – THWN-2 --- 2 black, 1 white, 1 Green (60’ each)
The green can be smaller - 10AWG, I think.
control wire – AWG # 14 or #12, need 150 – 250 feet (divided into 4 lengths) depends on Kohler supplied control wires – get colors to match Kohler’s colors if available
Check
Power wire for battery/heater - THWN-2 AWG # 12 - at least 60’, maybe double
Whatever the specs call for. I think you mean 2 12 AWG THWN @ 60'
PVC (Sched. 40) pipe for power and for control (buried in trench) plus connectors
Probably five 10’ lengths each (1¼ inch for power, ½ inch for control)
PVC conduit has a bell on one end of each section. The next section slides into the bell - no couplings needed. Yes, buy a couple in each size for insurance - you can always return them. A handful of male and female adapters in each size will save you a trip.
Hot tips: Lay the pipe with the bells pointing toward the end where you will feed the wire in. Also, if you don't have a pull tape, feed a length of mason's twine or jet line through each run as you make it up. Finally, always upsize pipe for ease of pulling. 1/2" conduit, especially, can be a PITA to pull through.
PVC (Sched 80) pipe/adapters/connectors to bring wires out of trench
Check. The Sch 80 to Sch 40 transition should be just a glue job.
We use a female adapter or a male adapter plus a rigid coupling to transition to a rigid 90 on each pipe at the generator end, but you don't have to.
PVC pipe cement
Solvent, check
Large/small flexible conduit for final run to Gen., into house and to transfer switch – about 15’ each
adapters to connect flexible conduit to Sched 80 pipe
What is it with the flex? A foot or two for the generator end, OK. You shouldn't need any at the house.
fittings to penetrate generator housing
?? It should at least have KOs.
fittings to penetrate house
Check, LBs
ground rod/strap/connector
and conductor, check
wire stripper for AWG #6 stranded wire
Sharp knife - utility knife. I bought a hawkbill, but I may do this a dozen or more times in a day.
may need end lugs for wire. If yes, need 4-8 lugs and crimping tool
Don't see why. See above.
200 Amp Service Cable – to go from transfer switch to main box – 10’ ?
Hmmm... Where are you locating the transfer switch relative to the service entrance and the panel? No unfused conductors in the open inside the house, ans as little as possible, total. We run individual conductors in conduit.
Penetration fittings for transfer switch – supplied by Kohler???
Maybe
Caution tape - required by inspector to inspect open 18" trench!
Yes, and gravel to lay under the pipe.

Sounds pretty complete. Phase tape, or are you buying colored wire for the 6 AWG?
 

Last edited by Nashkat1; 10-06-13 at 02:25 PM.
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Old 10-06-13, 07:51 AM
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Does Kohler still require an authorized dealer to be involved in the installation and startup for the labor part of their warranty to be effective?
 
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Old 10-06-13, 11:49 AM
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The hole and water trick sounds great but it won't work here in Rhode Island shale. The last time I drove one my friend and I pounded it with hand sledges for about 30 minutes.

Nashkat, really appreciate detailed response to the list! Very helpful.

The idea of using flexible conduit at the house penetration is because my plumbing skills are modest and I thought it would be better to have some play there.

The battery is in the generator housing, so the battery/heater wires will have to be pulled along with the control wires. Thought it would be easier to use single THWN wires in that case; had planned on using 1/2" PVC but will upsize if a test run is tight.

No KO's on the housing. The installation manual specifies a site for penetrations and provides a template for drilling or punching holes.

The transfer switch is going on a corner wall 1-2 feet from the main, close to where the service line comes in. I think (hope) I can reroute the service line to the TS without making any additional connections.

Don't know what I was thinking running cable back to the main. Will definitely use individual wires in conduit.

Thanks again guys. You are really a great resource.
Fred
 
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Old 10-06-13, 02:16 PM
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Yep, The quote I got from the Kohler dealer has a $300 charge for installation and startup.
 
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Old 10-06-13, 02:20 PM
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Just reread your last post Nashkat1. Gravel under the conduit? Do we have to dig so low that the top surface of the conduit is 18" down?
 
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Old 10-06-13, 03:19 PM
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Generator sited 45 feet from house - Require external disconnect? - will check with inspector. Anyone run into this?
Yep, sure have. Be sure to ask inspector on this. Some inspectors and some fire marshalls will require an accessible disconnect if there is either a lock or a special tool required to open the housing to access the output circuit breaker.
 
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Old 10-06-13, 08:38 PM
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Do we have to dig so low that the top surface of the conduit is 18" down?
Yes. Our standard at work is to dig 6" deeper for small conduit and 8" to 10" deeper for larger pipe.
 
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Old 10-10-13, 02:27 PM
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The green can be smaller - 10AWG, I think.
NashKat, missed this before. Where can I nail this down? Local inspector is mute.
 
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Old 10-10-13, 03:01 PM
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New Info (maybe just to me)

Just called a wire distributor for price per foot on THWN #6 wire. Nice guy let me know that they sell by the reel but that what I wanted was available at HD although they might not know they had it. Seems that new wire standard is THHN-2 which is rated 90 deg C both wet and dry. I was at HD and both the sign and electrical guy said that they carry only THHN so will go back and check that out tomorrow.
 
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Old 10-10-13, 04:01 PM
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Just called a wire distributor for price per foot on THWN #6 wire. Nice guy let me know that they sell by the reel
Before you buy at HD, I'd suggest you check with another supply house. Many supply houses sell #8 on up by the foot from 2500 foot reels in their warehouse. The big box stores will always be much higher on the wire.

I was at HD and both the sign and electrical guy said that they carry only THHN so will go back and check that out tomorrow.
Almost all THHN is dual rated as THHN/THWN. Type XHHW is also acceptable if you can find it.
 
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Old 10-10-13, 04:03 PM
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Check for buying by the foot with some internet sites. I was able to buy by the foot at a cost much less than HD even counting shipping.
 
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Old 10-12-13, 07:35 AM
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wire supply online

i self installed a generac 14kw. ********************
 

Last edited by Shadeladie; 10-12-13 at 08:34 AM.
 

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