Is this subpanel feeder acceptable?

[David J Smith]

I inspected a home today with 100 and 150 amp mains. The 100 amp main had a sub panel directly next to it supplying a small shop. The feeder for this sub panel is connected to the main panel using feeder conductor to lugs below the main shutoff. Is this acceptable and safe? I assume the main breaker provides some protection for the sub panel. This is not a code compliance inspection, but do not want this to come up again on another inspector's report. I already caught the neutral and grounds on same bar discrepancy, by the way. Thanks for your help. See photos.

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Here's another photo of the sub panel.

[Gunnar Alquist]

I inspected a home today with 100 and 150 amp mains. The 100 amp main had a sub panel directly next to it supplying a small shop. The feeder for this sub panel is connected to the main panel using feeder conductor to lugs below the main shutoff. Is this acceptable and safe? I assume the main breaker provides some protection for the sub panel. This is not a code compliance inspection, but do not want this to come up again on another inspector's report. I already caught the neutral and grounds on same bar discrepancy, by the way. Thanks for your help. See photos. Here's another photo of the sub panel.

Hi David,

I don't get how there can be two mains, one at 150 and the other at 100. I only see 100 amp mains. It may not be necessary for this discussion.

But, we will go from the panel in the 3rd pic, which seems to feed to the panel in the second pic. The feeder to the panel in the 2nd pic looks to be too small for the 100 amp breaker protecting it (more on that below). If so, I would write that up. A sub-feed breaker would not be necessary if the conductors were properly sized. Installing a properly sized breaker or changing the conductors is the likely solution.

I do seem to recall a 10 foot rule for feeders between panels. If I remember correctly, undersized was ok under certain circumstances. However, I am not certain about it and I'm too tired to look it up. Maybe someone will chime in and provide information or correct me.

Anyway, that would be beyond the scope of a home inspection. You should be deferring for the items noted as well as any discovered by the electrical contractor while making corrections.

[David J Smith]

Thank you for your input Mr. Alquist. You gave me helpful information. I referred this to an Electrician for further evaluation to cover myself. I had never encountered quite this scenerio.

[Jim Port]

The taps rules require OCP at the far end of the feeder which does not appear to be the case. It does look like the feedthrough lugs were used below the breaker to start the tap.

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The taps rules require OCP at the far end of the feeder which does not appear to be the case. It does look like the feedthrough lugs were used below the breaker to start the tap.

[Jerry Peck]

The taps rules require OCP at the far end of the feeder which does not appear to be the case. It does look like the feedthrough lugs were used below the breaker to start the tap.

That is in addition to the ground and neutrals bonded together on the same terminal bar in the shop panel.

[Gunnar Alquist]

The taps rules require OCP at the far end of the feeder which does not appear to be the case. It does look like the feedthrough lugs were used below the breaker to start the tap.


I thought a breaker was not required if the cables were adequately sized. Was I wrong?

[Jim Port]

I never use the tap rules since the conditions that allow their use can rarely be met, especially in residential.

[Jerry Peck]

I'll have to look them up, as Jim said, the tap rules are restrictive ... I was thinking that one of the restrictions was that the tap supplied a single breaker (as Jim also said) and a single item (not a panel), but I'll look them up.

[jack davenport]

From 2014 NEC Article 240.
Section 240.21(B)

(B) Feeder Taps. Conductors shall be permitted to be tapped, without overcurrent protection at the tap, to a feeder as specified in 240.21(B)(1) through (B)(5). The provisions of 240.4(B) shall not be permitted for tap conductors

(1) Taps Not over 3 m (10 ft) Long. If the length of the tap conductors does not exceed 3 m (10 ft) and the tap conductors comply with all of the following:


(1) The ampacity of the tap conductors is
a. Not less than the combined calculated loads on the circuits supplied by the tap conductors, and
b. Not less than the rating of the equipment containing an overcurrent device(s) supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors.


Exception to b: Where listed equipment, such as a surge protective device(s) [SPD(s)], is provided with specific instructions on minimum conductor sizing, the ampacity of the tap conductors supplying that equipment shall be permitted to be determined based on the manufacturer’s instructions.


(2) The tap conductors do not extend beyond the switchboard, switchgear, panelboard, disconnecting means, or control devices they supply.


(3) Except at the point of connection to the feeder, the tap conductors are enclosed in a raceway, which extends from the tap to the enclosure of an enclosed switchboard, switchgear,
a panelboard, or control devices, or to the back of an open switchboard.


(4) For field installations, if the tap conductors leave the enclosure or vault in which the tap is made, the ampacity of the tap conductors is not less than one-tenth of the rating of
the overcurrent device protecting the feeder conductors.

[jack davenport]

To qualify as a tap there are rules.

Basically to qualify as a legal 10' tap the tap conductors must be rated for 1/10 the ampacity of the overcurrent protection ahead of the tap. ( that 150 ampere main)

The tap conductors must not longer than 10' from termination to termination.

The tap conductors must be able to legally carry the combined calculated loads of the circuits the tap is feeding.

The tap conductors must terminate in an overcurrent protective device ( fuses/breakers)

The tap conductors must be in a raceway ( NM/SE/Ser cable is not allowed as it is not a raceway)

Taps can not use the "next size up" rule ( 240.4(B)) for sizing overcurrent protection. The conductor must be rated for the ampacity of the overcurrent protection it is terminated in.

Jerry - as an FYI - Taps can feed a panel, but the tap must be rated to carry the calculated loads of the circuits in the panel

Gunner - If the conductors are full size they are not tapped. It is a splice. Taps are when you use a smaller conductor tapped off a larger breaker like in the pictures. If they used a conductor rated for the 150 ampere main it would be considered a splice and a a main breaker would not be required .


Sounds confusing ? It is! Like Jim Port said it is difficult to apply the tap rules in a residential setting. Not saying it can not be done, (as it can) But it is often done incorrectly

[Jerry Peck]

From 2014 NEC Article 240.
Section 240.21(B)

(B) Feeder Taps. Conductors shall be permitted to be tapped, without overcurrent protection at the tap, to a feeder as specified in 240.21(B)(1) through (B)(5). The provisions of 240.4(B) shall not be permitted for tap conductors

(1) Taps Not over 3 m (10 ft) Long. If the length of the tap conductors does not exceed 3 m (10 ft) and the tap conductors comply with all of the following:


(1) The ampacity of the tap conductors is
a. Not less than the combined calculated loads on the circuits supplied by the tap conductors, and
b. Not less than the rating of the equipment containing an overcurrent device(s) supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors.


Exception to b: Where listed equipment, such as a surge protective device(s) [SPD(s)], is provided with specific instructions on minimum conductor sizing, the ampacity of the tap conductors supplying that equipment shall be permitted to be determined based on the manufacturer’s instructions.


(2) The tap conductors do not extend beyond the switchboard, switchgear, panelboard, disconnecting means, or control devices they supply.


(3) Except at the point of connection to the feeder, the tap conductors are enclosed in a raceway, which extends from the tap to the enclosure of an enclosed switchboard, switchgear,
a panelboard, or control devices, or to the back of an open switchboard.


(4) For field installations, if the tap conductors leave the enclosure or vault in which the tap is made, the ampacity of the tap conductors is not less than one-tenth of the rating of
the overcurrent device protecting the feeder conductors.

Thanks, Jack - seems as though item 3 is the one which seems to trip the contractors up the most ... based on what I recall seeing when they try to apply the tap rules in residential work.