Feeder Tap Leaves Panel Out to Disconnect. I say violation.

[don_resqcapt19]

I think you are confusing this with a circuit that is runnig on 40 amp on a 90 deg #10 , You would be correct , everthing involved would have to be 90 . Remember this is connected to a 30 amp disco and the load will never exceed 30 amp , We are talking about a fault current , The terminals wont have time to get hot the wire will blow into like a fuse link. It doesnt matter if you rate the wire 120

No confusion here. The ampacity of the wire under the rules of the NEC and the conditions of the install is 35 amps and the tap rule requires a conductor with an ampacity of 40. I don't see the fact that you have limited the load to 30 amps as changing the code ampacity of the wire.

 

[jumper]

common breackers are marked 40 deg c I guess you will say next cant rate wire 60 deg and connect to it ,

Here read this and tell what me you think.

 

[kwired]

I am saying that in systems of 600 volts or less it is a very very rare case where you can use the 90?C ampacity for anything other than derating. I am not sure about the split bolt, but as far as I know there are no equipment terminations rated for 90?C ampacities until you get to some very large equipment.

Many wire nuts are listed at 105C.

Seen many lugs with "AL9CU" marked on them. Been told the 9 means it is rated for 90 deg. I believe many neutral/ground bars in panelboards are 90 deg rated.

common breackers are marked 40 deg c I guess you will say next cant rate wire 60 deg and connect to it ,

The 40 deg rating is ambient temperature rating. The terminals are rated for 60 or 75 deg.

Glad you said that because it helps with the point I am trying to make , just because the wire wont go should not give you the right to reduce to # 10 in my opinion. A 1/0 could be tapped and connected to a 100 amp subpanel adjacent to the main 400 amp box and a 30 amp breaker installed . Industrial places can be very rough on a building moving pieces of steel on a hoist. If you never seen a piece of conduit pull a lose a #10 wire will virtually explode on a 400 amp breaker.

If you wish to put the 100 amp device between the 400 and 30 amp devices there is nothing wrong with that. Tapping a 10AWG off a 400 amp feeder with 10 foot tap rule is not allowed it would need to be 8AWG. You don't think 8 AWG that is 10 feet or less in length will carry fault current long enough to interrupt 400 amp OCD? The more fault current available the faster the OCD will operate. Back to the OP - the tap must be in a raceway. Likely this is for a little extra physical protection to the conductors that are protected above their ampacity - yet unprotected SE cable is allowed - go figure that one out.

The tap rules have had little or no changes for a very long time - there must not be too many bad incidents involving these rules.

 

[kwired]

Here read this and tell what me you think.

you beat me to it without even saying it.

from a post in the link:

btw, 40 C is the ambient rating. :smile: If you need to run it in a hotter ambient temperature you will have to derate the breaker itself. The manufacturer would aid you in figuring out the lowered rating above 40 C ambient.

I see long discussions with inspector if you do that. I'm not saying not to do that as I can see it as being a good design if done correctly, but many inspectors will see too large of a breaker for the conductor and will be very reluctant about letting it go.

 

[jetlag]

Seen many lugs with "AL9CU" marked on them. Been told the 9 means it is rated for 90 deg. I believe many neutral/ground bars in panelboards are 90 deg rated.



The 40 deg rating is ambient temperature rating. The terminals are rated for 60 or 75 deg.



If you wish to put the 100 amp device between the 400 and 30 amp devices there is nothing wrong with that. Tapping a 10AWG off a 400 amp feeder with 10 foot tap rule is not allowed it would need to be 8AWG. You don't think 8 AWG that is 10 feet or less in length will carry fault current long enough to interrupt 400 amp OCD? The more fault current available the faster the OCD will operate. Back to the OP - the tap must be in a raceway. Likely this is for a little extra physical protection to the conductors that are protected above their ampacity - yet unprotected SE cable is allowed - go figure that one out.

The tap rules have had little or no changes for a very long time - there must not be too many bad incidents involving these rules.

Yes I know a #8 will trip a 400 amp and so will #10 , in fact if you solve the formula for 240.92b for t (time ) you will find a # 10 will carry the 400 amp for 2.67 sec. , which is a lot more than the time it takes to trip a breaker. Notice the 60 or 90 deg choice makes no difference at all because T2 at the bottom which is damage limit for thermoplastic insulation is 150 deg c . Thats why I say you can use 90 for the 10 to 1 given in 240.21 .. Do you think the terminals have to be rated 150 to use 240.92 ? thats the argument for using the 90 rating. That has nothing to do with the load rating , a 10 can only serve thru a 30 a breaker except motor load. When I said the #10 would blow out I meant it would prob acr into at the point of damage. Show me where the code says you cant use 90 rate for tap (not load connection or breaker at disconnect) If help is needed with the formula I will be glad to show . Before condeming me give some thought to the 150 rate for the short circuit of tap . 60 or 90 has nothing to do with it

 

[jetlag]

I forgot to mention T1 in the formula is 60 c because the max load and breaker is 30 amp. I beleive this install of # 10 was shown on the original electrical plans, if the decision is left to an electrician in the field (including myself) they will go with a # 8 , no ones wants to bother with all this. We are discussing if its a violation or not . I say an electrical engineer will show it is not a violation as long as the disconnect is 30 and not 40. In the formula I = 400a . dont forget it has to be squared and so does the circular mil of 10380. I you dont have calculator with log10 their are charts on the internet , if you get
.1335389 you did it right log10 150+234/60+234 =.1335389

 

[IslandSparky]

Yes I know a #8 will trip a 400 amp and so will #10 , in fact if you solve the formula for 240.92b for t (time ) you will find a # 10 will carry the 400 amp for 2.67 sec. , which is a lot more than the time it takes to trip a breaker. Notice the 60 or 90 deg choice makes no difference at all because T2 at the bottom which is damage limit for thermoplastic insulation is 150 deg c . Thats why I say you can use 90 for the 10 to 1 given in 240.21 .. Do you think the terminals have to be rated 150 to use 240.92 ? thats the argument for using the 90 rating. That has nothing to do with the load rating , a 10 can only serve thru a 30 a breaker except motor load. When I said the #10 would blow out I meant it would prob acr into at the point of damage. Show me where the code says you cant use 90 rate for tap (not load connection or breaker at disconnect) If help is needed with the formula I will be glad to show . Before condeming me give some thought to the 150 rate for the short circuit of tap . 60 or 90 has nothing to do with it

Completely agree with your logic. Conductor/terminal temperature rating has no bearing on short-time withstand of the conductor. 10AWG is an acceptable minimum size. Personally though, I would always use an 8AWG to give myself a bit of a safety factor.

 

[kwired]

The tap still needs sized for 60 or 75 degree for the normal load current on the circuit, which is what it will be subject to most of the time. If you size it for 90 degree then it likely will be undersized for normal current conditions.

 

[iwire]

Completely agree with your logic. Conductor/terminal temperature rating has no bearing on short-time withstand of the conductor. 10AWG is an acceptable minimum size.

Logical or not still an NEC violation.

 

[kwired]

To add to my previous post we do not size circuit conductors for short time withstand conditions. Grounding conductors are often allowed to be smaller than the circuit conductors for this reason, but they are only intended to carry current for short time conditions.

 

[jetlag]

The tap still needs sized for 60 or 75 degree for the normal load current on the circuit, which is what it will be subject to most of the time. If you size it for 90 degree then it likely will be undersized for normal current conditions.

What , the normal load current is 30 amp max and connected to a 30 amp disconnect, we are sizing the tap for 60 deg load. How are we undersized for normal conditions.

 

[jetlag]

Logical or not still an NEC violation.

Show me where the code says choose only 60 , 75 conductors for taps, the code protects itself by limiting the breaker and load for the conductor 14 thru 10 . If you cant show the code it is usless to keep posting it

 

[jetlag]

To add to my previous post we do not size circuit conductors for short time withstand conditions. Grounding conductors are often allowed to be smaller than the circuit conductors for this reason, but they are only intended to carry current for short time conditions.

Oh we dont ? you need to read the intro to 240.92 b again , "Tap conductors are considered to be protected under SHORT CIRCUIT conditions when their SHORT CIRCUIT temperature (150 c for thermo plastic) is not exceed"

 

[iwire]

Show me where the code says choose only 60 , 75 conductors for taps, the code protects itself by limiting the breaker and load for the conductor 14 thru 10 . If you cant show the code it is usless to keep posting it

110.14(C) Temperature Limitations. The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination,

If you can't show the code that tells us 110.14(C) does not apply it is useless to keep ignoring it.

Or you could show us the under 600 volt equipment that is listed and labeled as suitable for 90C use.

 

[iwire]

Oh we dont ? you need to read the intro to 240.92 b again , "Tap conductors are considered to be protected under SHORT CIRCUIT conditions when their SHORT CIRCUIT temperature (150 c for thermo plastic) is not exceed"

None of the conductors you would be using are rated more than 90C.

 

[jetlag]

None of the conductors you would be using are rated more than 90C.

Man you are so lost , 150 is the short circuit limit for 60 75 90 deg thermo plastic, you dont use 150 rated wire in the formula . It means a tap must trip the breaker before the conductor goes over 150 or the insulation will be damaged

 

[don_resqcapt19]

Jetlag,
The issue here is that under the condutions of use, the #10 is does not have an ampcity of 40 amps. It must have an ampacity of 40 amps or more to be used in this application. The fact that it is being used at 30 amps and protected at 30 amps at the load end does not even enter into this. The fact that the wire is likely safe for this use also does not enter into this. The only thing that matters is the NEC ampacity of the conductor.

 

[iwire]

Man you are so lost , 150 is the short circuit limit for 60 75 90 deg thermo plastic, you dont use 150 rated wire in the formula . It means a tap must trip the breaker before the conductor goes over 150 or the insulation will be damaged

Can you show me this '150C rule' in the NEC?

 

[jetlag]

Can you show me this '150C rule' in the NEC?

All i can show you is Table 240.92 B calls it a tap short circuit current rating , and T2 represents the final temp allowed , and t 2 is shown at bottom for types of insulation and thermoplastic is rated at 150 c . It makes no distinction between tw 60 or thnn 90 , they are both thermoplastic. Notice that 240.92 B states taps specified in 240.21 B 2 are also allowed to be sized by 240.92 B . in other words 240.21 B2 does not have to be used. Also notice in the formula we dont use 90 for t1 because that is not allowed for the operating current of the circuit , instead we use 60. Refer to 310.10 frn which states the temp ratings shown in 310 are what conductors will stand for prolonged periods of time , it is not the short circuit rating or motor start rating. The point I am making is I have questioned tap sizes before that were 1 size smaller than allowed in 240.21 B2 and the owner showed me the original elec plans and informed me the tap can be sized differently under engineering supervision. So im saying the tap may not be a violation.

 

[don_resqcapt19]

... The point I am making is I have questioned tap sizes before that were 1 size smaller than allowed in 240.21 B2 and the owner showed me the original elec plans and informed me the tap can be sized differently under engineering supervision. So im saying the tap may not be a violation.

And you may very well be correct if the provisions of 240.92(B) apply.