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I have a newly built garage that I would like to add a sub panel. I have a QO load center QOB8-16L 100S which is rated for 100 amps. However, I think 60 amps would be more than adequate for my needs (1 20amp with 5 boxes, 1 20 amp dedicated to 10,000 BTU window Air conditioner, 1 15 amp circuit for 3 lights, 1 future 20 amp circuit to run to shed, 1 future 30 amp 240 volt circuit just in case) The total length of the run from the main service disconnect outside the house (200 amp) to the sub in the garage is about 60 ft. The sub in the garage is located adjacent to the pull up garage door. I've been told:

  1. can't tap at the service box outside the house;
  2. can't use split bolt connectors;
  3. can tap the load side of the 200 amp breaker using Polaris lugs and putting a disconnect on this feeder line immediately adjacent to the existing one.

The NEC on taps and feeders is somewhat confusing but looking at the section on outside feeder taps, it appears I should be able to do this without adding another disconnect at the house. The new feeder line would be protected by the 200 amp breaker which would be immediately upline of the Polaris lug. I would also install a backfed 60 amp breaker in the sub panel (or an AC disconnect) so I could disconnect everything there (normal AC disconnect does not provide over current protection). Service disconnect

Can I tap this way, or, what is the correct way to do it and what size wire should I use for the 60 ft underground run (direct bury cable, THHW or similar in conduit, or something else)? and what size Polaris lug to use (what size wire is used for 200 amp from the breaker to the inside the house). Also, do I need a ground rod at the garage? Thank you in advance for your responses and any enlightenment you may choose to shower on me.

Here is a picture of the meter and adjacent 200 amp disconnect. enter image description here

Service enters at meter. adjacent disconnect 200 amp to the right. Cable box is below meter. telephone box to left of cable box. It would be difficult to run from the house load center, as it is in the middle of the house. So, do the outside tap rules allow me to tap the load side of the 200 amp breaker and run it to a 60 amp main at the garage? The disconnect would be at the garage. Or would I Need to put a 60 amp disconnect next to the 200 amp box and run to the garage?

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    Is it a detached garage? How much more difficult would it be to run from the main service panel? Do you have space in that panel for 2 big breakers?
    – Harper - Reinstate Monica
    Commented Jul 21, 2019 at 2:16
  • you'd need to wire to the garage at a 200 amp rating to avoid another breaker since the existing one won't protect the wiring under a high amperage condition that is less than 200. it looks like there might be room in there for another breaker at 60 but probably not at 100. otherwise you need a bigger box. NEC tables should tell you the wire size for 100 (i don't have mine handy).
    – Skaperen
    Commented Jul 21, 2019 at 2:34
  • Where is the panel that disconnect feeds?
    – ThreePhaseEel
    Commented Jul 21, 2019 at 2:42
  • @Skaperen -- keep in mind the feeder tap rules....
    – ThreePhaseEel
    Commented Jul 21, 2019 at 2:42
  • Could you post a picture of the equipment just below the meter. It appears that the 200A breaker feeds that area? Or just a wider shot of the meter and panel showing the surrounding area.
    – Retired Master Electrician
    Commented Jul 21, 2019 at 13:43

2 Answers 2

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You can tap that at the protected side of the breaker.

the problem is many inspectors won’t allow use of the tap rules because of the length of the run and not supervised. Although allowed by 240.21.5 with the tap made at the breaker.

If supervision is the problem your wire would need to be rated for 200a even if it is going into a smaller panel or that’s what is normally required in my jurisdiction or one county.

What is supervised? Usually supervision means an industrial, commercial occupancy that requires license

a tap can be made with a listed lug or a 3 lug Polaris, one to the breaker and - to the house one to the garage. (Split bolts are normally 2 conductor not 3)

A tap conductor is similar to a service conductor in requirements for protection and the conductors having the ampacity of the single fused or breaker disconnect (a breaker panel with a main)

Since outside the conductors in conduit to the garage panel should be allowed sized to the main breaker per 240.21.5 1-4 with the exception of one of the counties I work in taps are allowed the other requires them to be sized to the breaker or in your case 200a worst case.

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I would install a 60a fusible disconnect to the right of that enclosure using a PVC nipple. Then polaris tap or insulation piercing tap both ungrounded and grounded conductors. Probably 1/0 between the tap and the line side of the disconnect would be sufficient. Also reemember to install a ground lug in the disconnect, keep the ground and neutral isolated in the disconnect and run the ground al the way back to the can on your picture.

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