Spider boxes

[Todd0x1]

The receptacles would b

The receptacles would be required to have OCP in accordance with 210.21. If they are 15 or 20 amp receptacles and the only protection O(other than being GFCI) is the 60 amp breaker it is definitely a violation.

Spider boxes (the yellow temporary power distribution boxes commonly used in construction and for events) have circuit breakers for the individual receptacles. Usually 6x 20A and 1ea 2P 30A feeding a L6-30R. There is a 50A CS twistlock inlet and passthrough receptacle. There is another version that has 60A 4P5W 120/208v 3ph pin and sleeve but those (and the cable) are really expensive so you don't see those often.

 

[Todd0x1]

they came off a 3ph 4W 60A branch circuit

In another post you mention theyre using the 50A spider boxes. Those are single phase with a 4 wire input, 2 hots, neutral, ground. How is this wired to the 60A 3ph circuit? Assuming they just used 2 hots. There should *really* be a 50A OCPD but I think some would argue that its not a very big deal.

 

[Isaiah]

In another post you mention theyre using the 50A spider boxes. Those are single phase with a 4 wire input, 2 hots, neutral, ground. How is this wired to the 60A 3ph circuit? Assuming they just used 2 hots. There should *really* be a 50A OCPD but I think some would argue that its not a very big deal.

I went out and checked again - you’re right they’re single phase 208V just like you stated. The cable is sized as #6AWG which is correct. Since they’re non continuous loads, you wouldn’t need to factor up 125% thus ideally it should be a 50A CB…here again I also don’t see this is a big issue. Many thanks for your input


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[Todd0x1]

I went out and checked again - you’re right they’re single phase 208V just like you stated. The cable is sized as #6AWG which is correct. Since they’re non continuous loads, you wouldn’t need to factor up 125% thus ideally it should be a 50A CB…here again I also don’t see this is a big issue. Many thanks for your input


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Well it should really be a 50A breaker due to the 50A connectors that exist downstream of it. But in practice whats that 10 amps going to do?

 

[Isaiah]

Well it should really be a 50A breaker due to the 50A connectors that exist downstream of it. But in practice whats that 10 amps going to do?

Keep in mind the CB is rated 80%, thus the need to size up 125%.


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[ggunn]

Temp Construction power - they came off a 3ph 4W 60A branch circuit and ran app 250’ to a spider box. From there they ran to second box 100’ away from the first and then to a 3rd box at another 100’ from the second. Each box has 3-5 extension cords at 120Vac to intermittent loads such as grinders and drills. All receptacles at the spider boxes have GFCI protection but it seems there would be a large voltage drop and potential overload scenario having all loads tied to single source over 400’ away. However the 60A CB has not yet tripped.

The distance (voltage drop) does not increase the current draw; it reduces it.

 

[Isaiah]

The distance does not increase the current draw; it reduces it.

Yes but the loads at three different distances. The cumulative ampacity is a grey area since loads are intermittent


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[Todd0x1]

Keep in mind the CB is rated 80%, thus the need to size up 125%.


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Can't protect the receptacle with a breaker larger than its rating.

210.21 Outlet Devices. Outlet devices shall have an ampere
rating that is not less than the load to be served and shall
comply with 210.21(A) and (B).

(B) Receptacles.
(1) Single Receptacle on an Individual Branch Circuit. A
single receptacle installed on an individual branch circuit shall
have an ampere rating not less than that of the branch circuit.

(3) Receptacle Ratings. Where connected to a branch circuit
supplying two or more receptacles or outlets, receptacle ratings
shall conform to the values listed in Table 210.21(B)(3), or,
where rated higher than 50 amperes, the receptacle rating shall
not be less than the branch-circuit rating.

Edit: this is from 2017 because I have a searchable pdf of it. I doubt these sections have changed.

 

[Isaiah]

Can't protect the receptacle with a breaker larger than its rating.

210.21 Outlet Devices. Outlet devices shall have an ampere
rating that is not less than the load to be served and shall
comply with 210.21(A) and (B).

(B) Receptacles.
(1) Single Receptacle on an Individual Branch Circuit. A
single receptacle installed on an individual branch circuit shall
have an ampere rating not less than that of the branch circuit.

(3) Receptacle Ratings. Where connected to a branch circuit
supplying two or more receptacles or outlets, receptacle ratings
shall conform to the values listed in Table 210.21(B)(3), or,
where rated higher than 50 amperes, the receptacle rating shall
not be less than the branch-circuit rating.

Edit: this is from 2017 because I have a searchable pdf of it. I doubt these sections have changed.

Yes but the boxes all have individual protection within the box


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[Todd0x1]

Yes but the boxes all have individual protection within the box


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not for the 50 amp connector

 

[Isaiah]

not for the 50 amp connector

Yes but I think the 60A will suffice in this case - 50A x 1.25% = 62.5A. The CB is only rated 80%
Not a perfect scenario admittedly

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[Todd0x1]

Yes but I think the 60A will suffice in this case - 50A x 1.25% = 62.5A. The CB is only rated 80%
Not a perfect scenario admittedly

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Still missing the point that, code wise, you cant put a 50 amp receptacle behind a 60 amp breaker.

In practice? -probably fine

 

[Isaiah]

Still missing the point that, code wise, you cant put a 50 amp receptacle behind a 60 amp breaker.

In practice? -probably fine

Please provide the article and section in code that talks to it - keep in mind the 50A connector at the box is not a receptacle


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[Todd0x1]

Please provide the article and section in code that talks to it


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I already did. 210.21. Here it is again:

210.21 Outlet Devices. Outlet devices shall have an ampere
rating that is not less than the load to be served and shall
comply with 210.21(A) and (B).

(B) Receptacles.
(1) Single Receptacle on an Individual Branch Circuit. A
single receptacle installed on an individual branch circuit shall
have an ampere rating not less than that of the branch circuit.

(3) Receptacle Ratings. Where connected to a branch circuit
supplying two or more receptacles or outlets, receptacle ratings
shall conform to the values listed in Table 210.21(B)(3), or,
where rated higher than 50 amperes, the receptacle rating shall
not be less than the branch-circuit rating.

Edit: this is from 2017 because I have a searchable pdf of it. I doubt these sections have changed.

 

[Isaiah]

I already did. 210.21. Here it is again:

210.21 Outlet Devices. Outlet devices shall have an ampere
rating that is not less than the load to be served and shall
comply with 210.21(A) and (B).

(B) Receptacles.
(1) Single Receptacle on an Individual Branch Circuit. A
single receptacle installed on an individual branch circuit shall
have an ampere rating not less than that of the branch circuit.

(3) Receptacle Ratings. Where connected to a branch circuit
supplying two or more receptacles or outlets, receptacle ratings
shall conform to the values listed in Table 210.21(B)(3), or,
where rated higher than 50 amperes, the receptacle rating shall
not be less than the branch-circuit rating.

Edit: this is from 2017 because I have a searchable pdf of it. I doubt these sections have changed.

The 50A connection to the box is an inlet - not a receptacle. It has a 50A feed thru at the opposite end


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[Todd0x1]

The 50A connection to the box is an inlet - not a receptacle. It has a 50A feed thru at the opposite end


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there's a receptacle somewhere between that inlet and the 60A breaker....

 

[Isaiah]

there's a receptacle somewhere between that inlet and the 60A breaker....

No sir… cable goes directly to the cb from the first 50A inlet


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[Todd0x1]

No sir… cable goes directly to the cb from the first 50A inlet


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what is on the end of the cable that is plugged into the inlet?

 

[Isaiah]

what is on the end of the cable that is plugged into the inlet?

The cable goes from the CB and has plug connector that goes into twist lock connection on the box. From there it branches into 20A and 30A CBs. All loads are properly protected.

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[Todd0x1]

The cable goes from the CB and has plug connector that goes into twist lock connection on the box.

And those connectors have to be supplied from a CB with a rating < or equal to the connector's rating. See table Table 210.21(B)(3) 50A receptacle is allowed to be on a 40A or 50A circuit and that's it.