When did rooftop table 310.15(B)(3)(c) appear in the code?

[Strathead]

As the subject states. Has this always been there, or was it added to ensure that people understood the impact of rooftop conduits? If it is a "newer" requirement, what were the restrictions before? I wonder because a contractor is asking us to remove and replace conduits for a reroof, at a location where I assume the Electrical Engineers were fairly diligent since about 1995. I feel that if we touch them though, any violation of this code will need to be accounted for. That calculates out to an adjustment factor of a whopping .58 :jawdrop:

 

[iwire]

As the subject states. Has this always been there, or was it added to ensure that people understood the impact of rooftop conduits? If it is a "newer" requirement, what were the restrictions before? I wonder because a contractor is asking us to remove and replace conduits for a reroof, at a location where I assume the Electrical Engineers were fairly diligent since about 1995. I feel that if we touch them though, any violation of this code will need to be accounted for. That calculates out to an adjustment factor of a whopping .58 :jawdrop:

There were no rooftop requirements. I think that table was added in 2002 or 2005.

I also seem to recall it is going away in 2017.

 

[mgookin]

As the subject states. Has this always been there, or was it added to ensure that people understood the impact of rooftop conduits? If it is a "newer" requirement, what were the restrictions before? I wonder because a contractor is asking us to remove and replace conduits for a reroof, at a location where I assume the Electrical Engineers were fairly diligent since about 1995. I feel that if we touch them though, any violation of this code will need to be accounted for. That calculates out to an adjustment factor of a whopping .58 :jawdrop:

My position is that you are not doing electrical construction which would compel compliance with new code. You are disconnecting conductors and raceway and moving them out of the way for roof replacement. You will put them back when the roofing is done.

You did not expand, enlarge or extend anything. You did not add load.

If it makes you feel better, consult your local electrical inspector. Any reasonable inspector should hold the same position. And if they don't, make him the bad guy and tell the roofing contractor it's going to cost more because the local electrical inspector says so.

 

[iwire]

Any reasonable inspector should hold the same position.

I think even a reasonable inspector could see it differently.

 

[Strathead]

I think even a reasonable inspector could see it differently.

Isn't it funny how we all look at things. You and I take 180 degree different approaches on the similar discussion and agree on this one. Just for the record, the reason I take this position on this subject is that you are putting your hands on the condition.

 

[iwire]

Isn't it funny how we all look at things. You and I take 180 degree different approaches on the similar discussion and agree on this one. Just for the record, the reason I take this position on this subject is that you are putting your hands on the condition.

We are all very different and are products of what we have delt with. We can still respect each other's views.

I often say, ask ten electricians how to do the same job and you will get ten different answers, the majority of them will be safe code compliant installations with maybe a couple of off the wall ideas.

 

[jap]

My position is that you are not doing electrical construction which would compel compliance with new code. You are disconnecting conductors and raceway and moving them out of the way for roof replacement. You will put them back when the roofing is done.

You did not expand, enlarge or extend anything. You did not add load.

If it makes you feel better, consult your local electrical inspector. Any reasonable inspector should hold the same position. And if they don't, make him the bad guy and tell the roofing contractor it's going to cost more because the local electrical inspector says so.

I cant recall one time we ever disconnected raceways and conductors on the roof and put them back exactly like they were without expanding or extending anything.
In this scenario, something almost always requires a change.

If your pricing it prior to doing the work, it would only make sense to make them aware of both options.
The roofer doesn't need to find this out the hard way.

JAP>

 

[Chamuit]

The rooftop adder was implemented in the 2008 NEC. I listened to most of the NEC Proposed changes webinar yesterday and it appears that the rooftop adder will be going away with the 2017 NEC. I agree that you should just go ahead and engage your AHJ inspector and get right from the horses mouth how he is going to want to handle this.

 

[petersonra]

The rooftop adder was implemented in the 2008 NEC. I listened to most of the NEC Proposed changes webinar yesterday and it appears that the rooftop adder will be going away with the 2017 NEC. I agree that you should just go ahead and engage your AHJ inspector and get right from the horses mouth how he is going to want to handle this.

why did they put it in and why are they now taking it out?

it seems to me that there has always been a requirement to account for higher than normal ambient temperatures even though it seems to be mostly ignored in attics and rooftops.

 

[iwire]

why did they put it in and why are they now taking it out?

I believe the wire manufactures asked for it and now it is being removed as there was no evidence it was a needed change.

 

[Chamuit]

why did they put it in and why are they now taking it out?

it seems to me that there has always been a requirement to account for higher than normal ambient temperatures even though it seems to be mostly ignored in attics and rooftops.

Remember the adder was in addition to the ambient temperature.

Apparently, from the information in the NEC webinar, the conduit basically provides thermal insulation from the reflected roof heat...something like that. And the imposition of the adder was not needed. I posted the webinar link here.

http://forums.mikeholt.com/showthread.php?t=177971

 

[don_resqcapt19]

I believe the wire manufactures asked for it and now it is being removed as there was no evidence it was a needed change.

The change was made based on the test results showing an increase in the conductor temperature where the raceway is installed close to the roof, however there was no evidence that these increased temperatures actually cause damage to the conductors or cause other problems. There was no problem to solve so there was no need for the original change....the CMP finally realized that in the 2017 process.

 

[ggunn]

The change was made based on the test results showing an increase in the conductor temperature where the raceway is installed close to the roof, however there was no evidence that these increased temperatures actually cause damage to the conductors or cause other problems. There was no problem to solve so there was no need for the original change....the CMP finally realized that in the 2017 process.

Then why derate for temperature at all? Anyone who puts conduit on a roof can tell you that conduits exposed to sunlight on a rooftop (and therefore the conductors inside it) get a whole lot hotter than the ambient temperature.

 

[ActionDave]

Then why derate for temperature at all? Anyone who puts conduit on a roof can tell you that conduits exposed to sunlight on a rooftop (and therefore the conductors inside it) get a whole lot hotter than the ambient temperature.

There is tons of wire installed on rooftops in the 60's, 70's, 80's, 90's, and early years of the 21st century, none of it that is in good shape is bursting into flames or otherwise failing.

Why derate at all?

Well, where is the real world evidence of a need to?

 

[ggunn]

There is tons of wire installed on rooftops in the 60's, 70's, 80's, 90's, and early years of the 21st century, none of it that is in good shape is bursting into flames or otherwise failing.

Why derate at all?

Well, where is the real world evidence of a need to?

It just doesn't make much sense to me to have different conductor ampacity derate numbers for every 5 degrees of ambient temperature and then disregard the substantial heating over ambient of conductors in conduit on rooftops exposed to sunlight.

 

[ActionDave]

It just doesn't make much sense to me to have different conductor ampacity derate numbers for every 5 degrees of ambient temperature and then disregard the substantial heating over ambient of conductors in conduit on rooftops exposed to sunlight.

Rooftops get hot? Really??!! When did this start?

 

[ggunn]

Rooftops get hot? Really??!! When did this start?

It started for me in 2008 when I began working in the solar (PV) industry.

 

[ActionDave]

It started for me in 2008 when I began working in the solar (PV) industry.

So, is there a real problem with real wires on real rooftops or is there an imagined problem coming from guys sitting in air conditioned offices (probably roof top units wired up with conductors sized pre 2008) crunching numbers on a computer?

 

[ggunn]

So, is there a real problem with real wires on real rooftops or is there an imagined problem coming from guys sitting in air conditioned offices (probably roof top units wired up with conductors sized pre 2008) crunching numbers on a computer?

It's not that there is a problem, per se. My issue is that if the ambient temperature is 100 degrees F we have to derate 90 degree conductors by 0.91; if the temperature on the roof is 140 degrees do we still derate the conductors by only 0.91? It doesn't make sense to me that we would derate the conductors for the temp difference between 80 degrees and 100 degrees but not for the difference between 100 degrees and 140 degrees even though the increase is twice as much.

 

[shortcircuit2]

It's not that there is a problem, per se. My issue is that if the ambient temperature is 100 degrees F we have to derate 90 degree conductors by 0.91; if the temperature on the roof is 140 degrees do we still derate the conductors by only 0.91? It doesn't make sense to me that we would derate the conductors for the temp difference between 80 degrees and 100 degrees but not for the difference between 100 degrees and 140 degrees even though the increase is twice as much.

I agree...and all they are doing is proposing the removal the table 310.15(B)(3)(c). The Code will still have tables 310.15(B)(2)(a) & (B)(2)(b) and they must be applied as applicable.