10' Tap Rule

[vw55]

I have a proposed installation that has a 225A panel tapped to a 400A panel 500kcmil feeder via 4/0 conductors. The 225A panel is provided with main lugs only, no main breaker.

The designer has indicated that this installation complies with 240-21(b)(1), the 10' tap rule.

My question is whether the intent of 384-16 can be circumvented using the tap rule. The 225A panel has no over current protection.

Another aspect of this installation is that the designer is using two 42 circuit sections sub-feed lug connected for each of the panels indicated and total connected load for both panels calculates 375A with spare breakers provided.

 

[milwaukeesteve]

Re: 10' Tap Rule

384.16 ??
I am lost on that one.

Following the tap rule, you would either need to feed this 225A panel with 400A conductors, or feed with 225A conductors and Backfeed a 225A breaker installed in that panel. Make sure you install a retention clip on the breaker.

 

[vw55]

Re: 10' Tap Rule

Sorry, the 384-16 reference is per 1999 N.E.C.

 

[infinity]

Re: 10' Tap Rule

I agree with Steve, either you use 400 amp conductors with a panel rated for 400 amps or you need overcurrent protection within 10 feet of the origin of the tap conductors.

[ April 27, 2005, 03:12 PM: Message edited by: infinity ]

 

[bob]

Re: 10' Tap Rule

The designer is correct. 240-21B.1 does not require a breaker. However 408.16 Overcurrent Protection for Panel Boards requires protection of the panel board by installing a breaker in the panel that has a rating not greater than the panel.

 

[milwaukeesteve]

Re: 10' Tap Rule

Bob, I miss the part of 240.21(B)(1) that says that this does not require a breaker.

[ April 27, 2005, 04:02 PM: Message edited by: milwaukeesteve ]

 

[jim dungar]

Re: 10' Tap Rule

If the panel is a "lighting and appliance branch circuit panel" then it requires a main OCPD. The main OCPD does not have to be integral to the panel, it may be mounted adjacent or even remote as long as it is "upstream".


Notes: Actually there can be (2) "main" OCPDs in the panel. This rule has been in effect as far back as I can remember(1975?).

 

[milwaukeesteve]

Re: 10' Tap Rule

Not disagreeing with you Jim, but could you spell out the distiction between lighting load and not in regards to this code rule.

 

[bob]

Re: 10' Tap Rule

Jim
408.14B spells out the requirement for OC protection for power panels. Why do these requirements call for an OC device.
IMO all panels should have protection.

Steve
408.14 A and B give the definition of Lighting and Power Panels. I wish someone would tell me why the distinction between them.

[ April 27, 2005, 05:33 PM: Message edited by: bob ]

 

[don_resqcapt19]

Re: 10' Tap Rule

Steve,

I miss the part of 240.21(B)(1) that says that this does not require a breaker.

The panel itself is a "device", so as long as the tap conductors have an ampacity equal to or greater than the rating of the panel, the rule in 240.21(B)(1) is satisfied. As others have said, the panel, if it is a lighting and appliance branch circuit panel, will have to be protected at or below its rating.
Don

 

[jim dungar]

Re: 10' Tap Rule

Steve,
It makes no difference what you or I call a "lighting" load. The NEC is only concerned with the number and rating of line to neutral loads.

Bob,
I won't argue with supplying a main OCPD for every panel, but I don't care if it is remote.

 

[bob]

Re: 10' Tap Rule

Jim
I agree with the remote OC for the panel. I was a little quick on the draw on that. You are correct.

 

[vw55]

Re: 10' Tap Rule

Don,

So you are saying that even though the tap rule has been satisfied, the panel still requires over current protection?

And could you please address the feed-through lug essentially providing 84 single pole circuit spaces? I am of the opinion that with no over current protection provided, there is a real possibility of overloading the 225A panel.

Thanks.

 

[milwaukeesteve]

Re: 10' Tap Rule

My question with the lighting load is that I don't see where the distinction is made in regards to the first rule listed for the tap conductors. The first rule wants the ampacity of the taps to be not less that the rating of the device OR not less that the rating of the overcurrent protection device...
My question to Jim and others is to why a lighting panel differs from others? 408.14 tells us the difference between the two, but where does article 240.21(B)(1) see the difference between the two? 408.14 does not describe either panel as a 'device'.
If we call the panel a device, then no, we don't need OCP. If we don't call it a device, then we do need OCP.
I haven't heard a panel described as a device before. Yes, it 'carries electricty but doesn't utilize electricity'(Art. 100). However, a panel is a distribution means and a controlling means (overcurrent/short circuit protection). I never heard of it described as a 'device'.

Another thing is that devices are regulated to keep from oversizing the circuit. You match the appropriate recept for the volts and ampacity of the circuit and load. You size switches appropriately, too. But when it comes to a panel with no OCP, there is almost nothing that would keep you from overloading that panel or those conductors. In this case we could theoretically run those 4/0's and that 225A panel up to 500A. What is there to stop us?

 

[don_resqcapt19]

Re: 10' Tap Rule

vw55,
There are two different rules here that must be complied with. One rule covers the required protection of the conductors and the other covers the required protection of the panel itself. If you use the tap rule and do not protect the conductors at their ampacity, you still must provide protection for the lighting and appliance branch circuit panel. As far as the feed through panel, the panels if they are lighting and appliance branch circuit panels must be protected at or below their rating.
Don

 

[don_resqcapt19]

Re: 10' Tap Rule

Steve,
When we are using the tap rules, we are in effect, placing the overload protection at the load end of the conductor and using the protection on the line side of the tap conductor to provide short circuit and ground fault protection. In the case of the 10' tap rule, there is no real protection from future overloads. In the original installation the tap conductor must have an ampacity equal to or greater than the combined computed loads on the circuits supplied by the tap conductors.
Don

 

[milwaukeesteve]

Re: 10' Tap Rule

Hey Don,
That rule has two parts. and (a) and a (b)
The first part is as you described about computed loads, but between (a) and (b) there is an 'and'. Part (b) talks about 'device'.
That is why I have a question about this.

 

[bob]

Re: 10' Tap Rule

milwaukeesteve

In the definitions device is A unit of an electrical system that is intended to carry but not use electric energy.

 

[milwaukeesteve]

Re: 10' Tap Rule

Is a distribution panel a device?
If you can convince me of that I would agree, but again, I have a hard time seeing something that controls, regulates, protects and distributes electricity as meeting the definition of device. I am comfortable with all those words except for 'distributes'. I don't believe that is what Art 100 describes a device as.

 

[don_resqcapt19]

Re: 10' Tap Rule

In my opinion an MLO panel is a device.
Don