# I guess I don't understand temperature rating compatibility



## 99cents (Aug 20, 2012)

The 2012 CEC has these rules requiring compatibility between the conductor and protective device temperature ratings. Fair enough but, if I look at the following information from the BC Safety Authority, we are allowed to install a junction box inside a building and splice 75 degree service conductors to 90 degree conductors in order to make the conductor and breaker compatible.

Can somebody explain the logic behind these temperature ratings? It seems to me that making a splice ahead of a panel is just...well....something I normally don't do. Making splices around a panel to change conductor size seems like the symptoms are worse than the disease.

Thanks.

http://safetyauthority.ca/sites/default/files/Module2Handout2012ElectricalCodeChangesFinal_3.pdf


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## Semi-Ret Electrician (Nov 10, 2011)

Someone installed a long feeder using the 90 deg col. instead of the 75 deg. and asked me what they could do to salvage the install.

I suggested they do what you said: splice to the run with 90 deg. connectors and a few inches of 90 deg wire to the 75 deg term.

It passed inspection but IMO was really just a loophole in the Code and not very good engineering.


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## 99cents (Aug 20, 2012)

This rule just applies to service conductors. Maybe it's one of those band-aid rules that says you don't have to run new underground cable just to meet the requirements. It just seems odd to me.

Keep in mind this is Canada, the country that took a perfectly good code book and screwed it up, an opinion that inspectors seem to agree with..


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## Semi-Ret Electrician (Nov 10, 2011)

99cents said:


> This rule just applies to *service conductors*. Maybe it's one of those band-aid rules that says you don't have to run new underground cable just to meet the requirements. It just seems odd to me.
> 
> Keep in mind this is Canada, the country that took a perfectly good code book and screwed it up, an opinion that inspectors seem to agree with..


Around here the POCO has no problem splicing our 4/0 AL service conductors to their #6 AL service drop.:laughing:


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## chicken steve (Mar 22, 2011)

99cents said:


> The 2012 CEC has these rules requiring compatibility between the conductor and protective device temperature ratings. Fair enough but, if I look at the following information from the BC Safety Authority, we are allowed to install a junction box inside a building and splice 75 degree service conductors to 90 degree conductors in order to make the conductor and breaker compatible.
> 
> Can somebody explain the logic behind these temperature ratings? It seems to me that making a splice ahead of a panel is just...well....something I normally don't do. Making splices around a panel to change conductor size seems like the symptoms are worse than the disease.
> 
> ...


Interesting pdf 99*

Our temp ratings are basically predicated on whatever we're terminating a conductor to

Not much is rated to be run continuosly @ 90C (167F because i can't think metric) , maybe some service equipment .....




*your MBJ locations seem euro....? 

~CS~


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## chicken steve (Mar 22, 2011)

Semi-Ret Electrician said:


> Around here the POCO has no problem splicing our 4/0 AL service conductors to their #6 AL service drop.:laughing:



#6 to 500kcmil on my last 400A upgrade!

~CS~


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## 99cents (Aug 20, 2012)

chicken steve said:


> Interesting pdf 99*
> 
> Our temp ratings are basically predicated on whatever we're terminating a conductor to
> 
> ...


So, theoretically, you could splice a pigtail ahead of (or behind) a breaker and you're good to go? I know that sounds stupid so what is the reasoning behind the temperature compatibility? We just adopted this nonsense two months ago. Maybe (??) if I understand I won't call it nonsense.

After re-reading your post, your temp rating is based on the temp rating of the connected load AND the protective device? This is turning my brain to mush...


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## FrunkSlammer (Aug 31, 2013)

I'm sure Mshea could explain this better than anyone.. I remember having it explained to me, but I didn't understand it well enough to retain the concept.

It had something to do with the heat build up on the conductor at the lug termination point... 

The end. lol It could be the holidays and all the eating and drinking, but I can't recall much more than that.


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## 99cents (Aug 20, 2012)

FrunkSlammer said:


> I'm sure Mshea could explain this better than anyone.. I remember having it explained to me, but I didn't understand it well enough to retain the concept.
> 
> It had something to do with the heat build up on the conductor at the lug termination point...
> 
> The end. lol It could be the holidays and all the eating and drinking, but I can't recall much more than that.


So, if the terminals in your JB are rated 90 degrees C, then the rule almost makes sense (assuming that terminals have a temperature rating or a default of 90 degrees C).

I am still not understanding this, though. You can have the same size of conductor with different temperature ratings depending on insulation type. If the concern is heat build up at the termination point, you obviously have to strip the insulation off to make your connection. What difference does insulation value make?

If it's possible, my brain is getting mushier...


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## 99cents (Aug 20, 2012)

chicken steve said:


> Interesting pdf 99*
> 
> Our temp ratings are basically predicated on whatever we're terminating a conductor to
> 
> ...


Must be that free trade agreement we signed in Brussels.


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## FrunkSlammer (Aug 31, 2013)

I think the idea is that if you use a 75c conductor to get the same ampacity as the 90c conductor, it will probably be one size up. So the heat build up is either less, or the increased area helps with cooling, I don't really get it either.. just trying to help.


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## Big John (May 23, 2010)

FrunkSlammer said:


> I think the idea is that if you use a 75c conductor to get the same ampacity as the 90c conductor, it will probably be one size up. So the heat build up is either less, or the increased area helps with cooling....


 That's my understanding.

Remember that conductor temperatures are determined by how well the insulation resists heat. That's why the ampacity tables have different allowable limits for the same AWG. 

If you increase the conductor size, you reduce the conductor resistance, reduce the I²R losses which reduces the heat that the conductor will produce.

This in-turn reduces the the heat that will be transmitted to the termination at the end of the conductor, and ensures that it is not over-temp.

I don't know how many feet are necessary to actually change the temperature that the lug sees, but I agree with _Semiretired _that adding a couple inches of the correct conductor is basically a loophole and probably isn't technically correct.


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## chicken steve (Mar 22, 2011)

For ex, adding a few inches of modern 90C wire to say, ancient K&T creates that 'poorly engineered' _grey area_ that allows us to terminate new fixtures ..........

~CS~


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## Semi-Ret Electrician (Nov 10, 2011)

chicken steve said:


> #6 to 500kcmil on my last 400A upgrade!
> 
> ~CS~


lol I did a 400A upgrade like that and when the POCO tried to do that I stopped him and asked if he say anything "funny" with that.

He called his boss to the site and I shamed him into a heavier drop. 

POCO may be the cause of "Global Warming" with their "Caloric Service Drops"


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## 99cents (Aug 20, 2012)

FrunkSlammer said:


> I think the idea is that if you use a 75c conductor to get the same ampacity as the 90c conductor, it will probably be one size up. So the heat build up is either less, or the increased area helps with cooling, I don't really get it either.. just trying to help.


Actually, that makes sense. It probably reduces hot spots in the panel. And, in those rare cases where 75 and 90 degree ampacities are equal, common sense would say you can go with the R90 (I hope).


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## Semi-Ret Electrician (Nov 10, 2011)

Big John said:


> That's my understanding.
> 
> Remember that conductor temperatures are determined by how well the insulation resists heat. That's why the ampacity tables have different allowable limits for the same AWG.
> 
> ...


IMO a breaker will actually heat the conductor. Many times I've measured the higher temperature at the termination than a few feet down the wire.

Probably because of the slight contact resistance and a less than perfect torque in the connector. Both usually exceed the I^2 R losses in the wire.


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## Big John (May 23, 2010)

Semi-Ret Electrician said:


> IMO a breaker will actually heat the conductor. Many times I've measured the higher temperature at the termination than a few feet down the wire....


 Agreed. Breakers and the associated terminals are temperature tested with a 4 foot length of conductor attached. I believe the idea is that conductor will act as a heat sink (and I think Zog has confirmed that). So if the conductor is already operating above rated lug temperature, obviously it's not going to dissipate heat as intended, and it increases the overall temperature that everything will be exposed to.

I say all this, but it's not common for me to see properly-working low-voltage equipment operating near temperature limits to begin with.


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## Bugz11B (May 12, 2013)

I almost always use the 75 deg C col for sizing circuits because I am yet to see terminals rated for 90 deg (I do 99% homes, may have higher terminal ratings elsewhere), I only use the 90 deg col for derating. 



chicken steve said:


> For ex, adding a few inches of modern 90C wire to say, ancient K&T creates that 'poorly engineered' _grey area_ that allows us to terminate new fixtures ..........
> 
> ~CS~


Im not sure im understanding this correct, let me see, is this saying that you can tie a #12 thhn to a #12 TW and then use the 90 deg col for the circuit? If so thats 100% not allowed here in Florida you must size your circuit based on the weakest insulation rating in that circuit in this case the entire circuit must be sized off the 60 deg col (which makes perfect sense)


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## Big John (May 23, 2010)

Bugz11B said:


> Im not sure im understanding this correct, let me see, is this saying that you can tie a #12 thhn to a #12 TW and then use the 90 deg col for the circuit? If so thats 100% not allowed here in Florida you must size your circuit based on the weakest insulation rating in that circuit in this case the entire circuit must be sized off the 60 deg col (which makes perfect sense)


 Agreed, it's an NEC violation. 110.14(C) says that you can't exceed the lowest temperature rating of any part of the circuit.

But for example, _Frunk _was talking about upsizing a lower temperature conductor to match the same ampacity as the higher temperature conductor, which would be legal.


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## FrunkSlammer (Aug 31, 2013)

CEC just started using this whole new temperature rating system based on insulation and equipment. The old system we didn't have to think about anything, just look at the chart and use the ampacity.. _maybe_ apply a voltage drop derating and multi conductor derating. 

*OLD*









*NEW*







Big differences. Now we have to use the new rules to make old installs jive.. it's tricky even if you even understand the new rules!


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