Whole home manual Generator interlock install

A generator interlock is essential equipment when using a portable generator to power your home. The interlock allows you to backfeed power into your electrical panel through a dedicated breaker that can only be turned on if the incoming utility power is turned off. This prevents power from being applied to the grid which would present an electrocution hazard to power line workers.

The complete interlock setup consists of:

  1. an incoming power connector (inlet),
  2. “back feed” breaker,
  3. and a manual sliding plate to prevent power from two locations at once (interlock) all wired together.

Many people install their generator power inlet box right next to their power meter. Doing so provides the fastest installation and lowest cost.

I opted to locate my generator inlet box about 65 feet away next to my grill on a covered patio. What does this accomplish?

  • I can run my generator in the rain or other poor weather without worrying about it shorting out.
  • It’s in a fenced in area behind the house where I can keep an eye on it and would be thieves can’t roll it away.
  • It’s next to the natural gas outlet I installed for the grill. Eventually, I’ll add a special regulator to the generator and have an infinite supply of cheap clean fuel.

So in my mind this was well worth the extra cost which all told was only an extra $150 in conduit & wire and a few extra supplies.

Here is a complete breakdown of expected costs.

Item(s) Total Cost 
6 gague THHN Green, Black, Red, White wire 100 ft x 4 $          249.98
Conduit, conduit hooks, screws, & solvent glue.  $          150.00
SDS concrete drill bit $             42.99
Electrician Fish tape – (i ended up not needing) $          100.00
Mechanical Interlock $             69.95
Power inlet cord Generator > House $          100.00
Outdoor Power Inlet Box w/ 50 amp connector $             71.56
Electrical Permit $          120.00
Total(s) $          904.48

I did start in the same location though as most. I opted to start from the main outdoor breaker panel and work back to the patio location.

Note any potential areas on your electrical panel where other conduits are already in place.

Step 1 – survey available spaces on bottom of panel making sure you find the most ideal space to add another conduit run. Mine already had 2 conduits sticking out the bottom.

Step 2 – Disconnect power and remove dead front. IF You have ANY doubts about what you are doing here STOP and get help from a LICENSED electrician or your power company. A “dead front” is the panel that covers the live component terminals to prevent you from getting shocked. Per code you can’t have any holes in it that are not “filled” so exercise caution when removing blank spots from your dead front.

Remove the “dead front” panel protecting breakers and bus. In this photo power is on and there ate LETHAL voltages present. DO NOT touch copper plated bus bars or beaker contacts. You will get shocked / possibly killed. IF You have ANY doubts about what you are doing here STOP and get help from a LICENSED electrician.

Reminder…As a homeowner you still need to comply with all local and federal laws regarding your installation. In many locations this type of project requires an electrical permit by the “AHJ” or “Authority Having Jurisdiction.” This will help make sure you are doing everything right and safe.

If you ever have a major insurance claim or liability issue with your home please know that it is very likely that a forensic investigation will occur to determine if the root cause was due to negligence which is not covered in most situations.

Note that almost everything manufactured has date codes stamped on them including wire and conduits. In most cases with electrical work it is fairly easy to determine if work that required a permit was not permitted.

Note where the conduits lead under the house.

I spent some time under the house in the crawl space determining where my new hole would appear before starting to drill. You don’t want to accidentally drill into a wire, drain, water pipe, gas line, or some structural component holding your house up!

Step 3 – If your power will be in another location than next to the distribution panel, drill any holes needed for conduit travel from point “A” to point “B.”

Concrete core drill bit with SDS arbor attachment and pilot bit purchased on Amazon.
I really like the cordless SDS drill. It can hammer, drill, or hammer and drill. It works fast too.

I used a 1.5” core drill to cut through both brick and cinder block. Supposedly a 1-3/8” hole is big enough for 1” schedule 40 PVC conduit. I wanted a little “wiggle room” just in case. It turns out the smaller hole would have worked ok. A little caulk will seal any gaps.

I ended up having to trim a holly bush that got in my way. The sawzall made fast work of it.

Step 4 – run & connect conduit paths from point “A” to point “B.”

These ratcheting pvc tubing cutters look like they shouldn’t be be able to cut 1” diameter pipe. They cut it like butter.

Dry fit pvc assemblies before gluing together.

Use a screwdriver or other tool to knock out the pre punched hole closest to where your pvc conduit needs to line up,
Hole is not big enough for 1” conduit coupler.
Move any ground or power wires out of the way so you don’t damage them.
I didn’t want to go overboard on hole size so I kept checking until I got it just right.
Tighten the retainer nut by hitting the little edges with a flathead screwdriver until the coupler is tight.
In most areas, primed PVC joints are code required. The way an inspector knows they are primed is by the purple dye in the primer. Prime before you use cement.
Notice I vacuumed out the metal chips from my enlarged hole? My favorite tool is my cordless ridgid shop vac.
Glued conduit body. These help you pull wires through 90 degree turns. Essential!

Step 5 – install your manual interlock. align the dead front carefully to make sure it will actually work. If you are off slightly it can cause the unit to not work as intended defeating the purpose of your project.

Use a punch to make sure your holes don’t wander off center!
Screws inserted through back of panel.
Install any provided stickers. they are just as much a part of complying with NEC code as the rest of the project.
Straighten your cables before pulling them and the pulling will go easy. I (pushed) pulled ~75 linear feet of these (Qty 4) 6 gauge wires without an electricians fish tape. Heavier gauge wires can be pushed and pulled because of their firmness.
Keep your wires separated while pulling and they will pull easier.
I did away with the pilot bit on the second hole. I found that not using a pilot bit and starting slow created a smooth hole.
Hole done. Again know where you are drilling. I clearly was near a gas pipe here.
sometimes you have to invent the bit you need.
Make sure all conduit is fastened with metal straps at appropriate intervals.
Wires pulled into distribution panel prior to trimming.
I had extra conduit straps so each joist got one. This conduit is not moving!
“S” type bend for easy cable pulling through a turn.
Get the conduit body tight against the wall.
Inlet box mounted to wall with Tapcon concrete anchors
THHN wire pulled into position.
I added a ground bus to this box.

The ground bus i added (small aluminum block) was complete overkill. But from an engineering standpoint i wanted this to be safe. In the event a wire came undone, in theory the wire could electrify the box and shock someone. Now everything metal is grounded to the same potential.

the gas pipe next to this was annoying me because I never painted it gray.
Pipe painted. Problem solved.

Use cable ties to strap the breakers together to make sure they stay in place and secure!

Last step – put the dead front back on and call the inspector then test!

Note the APPROVED Inspection label after the inspector came out.

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