- Location
- Massachusetts
Dennis Alwon said:
Well we do not know that the additional conductors will be current carrying conductors.
derate wires
- Thread starter Rewire
- Start date
- Status
Well we do not know that the additional conductors will be current carrying conductors.
The only reason I could see for installing "spare" conductors, would be that the plans/specifications call for them. Otherwise it would be like sticking dollar bills in the conduit before leaving the job... If they are being installed just to meet a requirement of the plans, I would not count them as current carrying conductors as the probability is that they will never be used.
frizbeedog
Senior Member
- Location
- Oregon
haskindm said:
....and then the customer calls you up and says he's ready to have those good ol wires you installed last year heated up and connected. And you say, uh...well...you see...it's like this; I'd love to but I can't. The reason is you asked for it, and I did it but...well, it's complicated. I have to replace that conduit and all those wires and it's going to cost you this much. As you spead your arms wide to show him how much. And then he finds another contracotor who will heat them up and connect them. So not only have you not given your customer good service but the next guy will jump all over it thinking "WOW, look at this! those swell guys who came before us were really considerate." And then...
Wait...that's the next guys problem. Either way, you're the next guy, and it's a problem.:grin:
- Location
- Massachusetts
frizbeedog said:
So how much money do you give away when not required to?
frizbeedog
Senior Member
- Location
- Oregon
iwire said:
None. Say the customer asked for the extra wires.
cschmid
Senior Member
- Location
- Northern cold country
interesting I have pulled several pipes with extra wires in them..We derate the wires the only reason they are there is for further use and normally pulled in due to length of run and the sensitivity of the equipment being supplied..that way we can make modifications on the run with out shutting everything down to pull couple extra wires..normally in a commercial or industrial setting this is done..You derate them due to the fact they are going to carry current other wise why install them very few dry contact switches placed that way..dry contact = non powered..if you run non powered switches in conduit with several other current carrying conductors you can in up with induced voltage and that i whole new problem..So normally when this is done they are going to be current carrying conductors..unless it is one just so you can pull in new wires with it..
haskindm said:
I pull an extra conductor every once in a while (depending on the install) for two reasons:
1) if a conductor gets damaged
2) if something is added later
when I pull them, I don't overfill though, I think that's ignorant
I would never, however, inform a customer (even on a set of as builts), that there were extra conductors in there, because stupid questions would always follow, and if I pulled it in for free, I have every right to charge them for it later when I use it. they never need to know. to my knowledge, noone has ever had a problem with this.
Local26 Sean
Member
If you pull extra conductors into a raceway, haven't you already decided that they will carry current at some point?
Why on earth would you pull a spare that, if used, makes the install a violation?
In my opinion, If you are working for a regular customer, I'd say use bigger conduit, and make the install legal with the spares included.
If the job is a one shot deal, Just do it correctly and forget spares.
Why on earth would you pull a spare that, if used, makes the install a violation?
In my opinion, If you are working for a regular customer, I'd say use bigger conduit, and make the install legal with the spares included.
If the job is a one shot deal, Just do it correctly and forget spares.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
You are confusing minimum code requirements and good design practice. I agree that if I put spares in a conduit, it is a good idea to size the conductors under the presumption that all will be current-carrying some day. When that future install is done, the owner will be happy that I made that precautionary extra step. But the code does not require me to do it, and the code does not care if the owner is happy.Local26 Sean said:
On large industrial jobs it is very normal to pull extra conductors in conduit, as it is to have spares in multi conductor cables. A 12 donductor installed, and maybe 8 conductors used. And when you terminate, you keep the conductor long enough to reach any termination point in the cabinet. Things do change! A well thought out installation makes those changes easier.
- Location
- Massachusetts
Local26 Sean said:
No.
Just because a conductor may carry current does not always means it will be a current carrying conductor to the NEC.
Control circuit, non simultaneous operations, neutrals etc are all examples of conductors that carry current but are not always current carrying conductors as far as derating.
The ability of insulated wire to carry rated current is dependent on the temperature of said insulation. That is, as current increases through a conductor it gets warmer, and that heat is dissipated through the insulation. When the temperature of the insulation is at it's rating, it begins to degrade... and higher temperatures make it degrade perhaps at an exponentially faster rate.dcooper said:
So far the discussion has only been concerning one insulated conductor. When you put several in close proximity within the confines of a raceway, the heat generated by current passing through each conductor cannot be dissipated as fast as it can with one conductor, i.e. more heat is being generated but same rate of dissipation. Therefore, the temperature rises faster and can exceed the insulation's rating if all conductors are passing the table-rated amount of current.
Last edited:
- Location
- Massachusetts
dcooper said:
To add to Smart's good explanation.
First we need to remember that all conductors carrying current generate heat, how much heat depends on the amount of current.
Picture standing by yourself in a room without ventaltion or cooling, the temperature is good and you feel comfortable.
Now fill the room with other people.
Will you become uncomfortable hot?
Each persons heat will add to the total heat in the room. The same happens with multiple conductors in a raceway.
mike grisofe
Member
Spare Conductor - Why ?
Spare Conductor - Why ?
Pull in jet line for future additions - Save money.
Spare Conductor - Why ?
Pull in jet line for future additions - Save money.
- Location
- Massachusetts
dcooper said:
No it is not 'already deratated'.
The derating rules apply to NM just like conductors in pipe.
However....334.80 allows us to start our derating calculations at the 90 c rating
What this means is you can bundle 12/2 NM without an issue until you get to 9 total current carrying conductors.
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
The OP's question is a very good question. I had to really think about it and read over 310.15(B)(2)(a) again - which I have only read many times before.
The short answer I have is, derating for conductors that are not carrying current is not required.
Spare conductors do not carry current -unless we count induced current :wink: .
The other portion of my answer is just some musing...
If the number of actual current carrying conductors is such that adding any other conductors (such as spares) would require a reduction in ampacity or increase in size of the existing conductors already installed as part of the initial install. The company/engineer who designs this really has little or no principles.
The short answer I have is, derating for conductors that are not carrying current is not required.
Spare conductors do not carry current -unless we count induced current :wink: .
The other portion of my answer is just some musing...
If the number of actual current carrying conductors is such that adding any other conductors (such as spares) would require a reduction in ampacity or increase in size of the existing conductors already installed as part of the initial install. The company/engineer who designs this really has little or no principles.
- Status