100% ocpd

[TonyThunder]

If I use a 100% rated over current protection device for a lighting circuit, then I know I can keep my conductors at the non-continuous and continuous load, intead of non-continuous and 125% of continuous load. But do I still need to derate the conductors for mutal heating, more than 3 conductors, and for ambient temperature, greater than 75 degrees F? I'm thinking that I must still do this but there is an article, I think 215(?), that seems to indicate that with a 100% rated OCPD, no derating of the condcutor is required.

 

[kwired]

If I use a 100% rated over current protection device for a lighting circuit, then I know I can keep my conductors at the non-continuous and continuous load, intead of non-continuous and 125% of continuous load. But do I still need to derate the conductors for mutal heating, more than 3 conductors, and for ambient temperature, greater than 75 degrees F? I'm thinking that I must still do this but there is an article, I think 215(?), that seems to indicate that with a 100% rated OCPD, no derating of the condcutor is required.

The first step of sizing conductors is to determine minimum size required by device terminals. 100% rated devices do not require sizing to 125% for continuous load because the terminals are designed to "heat sink" more heat than non 100% rated devices. Good luck finding this type of device for your typical lighting circuit. If terminal temperature is 60 degrees then you must use 60 degree column of T310.16 even if you are using 90 degree insulated conductors. This sizes for conductor to the operating temperature of the terminations.

The next step of sizing conductors is to determine minimum size required by conductor insulation. This is where ambient temperature corrections, and multiple conductors in a raceway corrections come into play. If using 90 degree insulation you can use 90 degree columns in T310.16 for this part. You must derate for these conditions no matter what you have in the first step. This sizes for conductor insulation operating temperature.

The third part of sizing conductors is to select the larger of the two conductors determined in the first two steps - this is your minimum conductor size.

Add:

110.14 mentions electrical connections requirements

310.15 covers temperature derations.

 

[jim dungar]

I know of no manufacturer that makes a 100% rated breaker that is not at least a 200A frame size and does not have an electronic trip.

I cannot remember any installation where it was cost effective to use a 100% rated breaker smaller than 800A.

Conductor ampacity must always be adjusted based on the number in the raceway and the ambient air, regardless of the insulation class.

 

[TonyThunder]

Thanks concerning the cost of the 100% rated OCPD.

 

[templdl]

This is who have looked at the application of 100% rated breakers.
As one of the other poster said the OCPD will have a solid state trip.
Regarding calculating the load, to size the condictor for application with a 100% rated device, yes, it is in fact computed using 100% of the continuous load plus 100% of the non-continuous load. Then you select the cable size base upon the 75degC column. HOWEVER!! You must use 90deg insulated cable! Then, the 100% rated device must be used in a suitable enclosure following the manufactures instructions.

Please remember that 100% rated devices are no better than the 80%. What a 100% rated device is able to get you is the posibility of using a smaller cable depending upon where the ampacity falls within the cable ratings by not having to add that extra 25% for the continuous load. Then the OCPD is sized based upon the actual cable rating using 75deg C (not 90degC). This gives you a second opportunity to select a smaller frame size OCPD which may also save money.
The bottom line is that you must run the numbers is order to see what your savings would be.

 

[kwired]

This is who have looked at the application of 100% rated breakers.
As one of the other poster said the OCPD will have a solid state trip.
Regarding calculating the load, to size the condictor for application with a 100% rated device, yes, it is in fact computed using 100% of the continuous load plus 100% of the non-continuous load. Then you select the cable size base upon the 75degC column. HOWEVER!! You must use 90deg insulated cable! Then, the 100% rated device must be used in a suitable enclosure following the manufactures instructions.

Please remember that 100% rated devices are no better than the 80%. What a 100% rated device is able to get you is the posibility of using a smaller cable depending upon where the ampacity falls within the cable ratings by not having to add that extra 25% for the continuous load. Then the OCPD is sized based upon the actual cable rating using 75deg C (not 90degC). This gives you a second opportunity to select a smaller frame size OCPD which may also save money.
The bottom line is that you must run the numbers is order to see what your savings would be.

Unless the manufacturer instructions say this where do you find this information. According to NEC if it is a 75 degree terminal you must use 75 degree ampacity value minimum, 90 degree conductors are acceptable but at 75 degree values.

 

[jim dungar]

UL does not list any overcurrent protective device for use with conductors sized using the 90?C ampacities (although some switchgear, ANSI construction is).

 

[kwired]

UL does not list any overcurrent protective device for use with conductors sized using the 90?C ampacities (although some switchgear, ANSI construction is).

templdl stated you must use 90 degree conductors at 75 degree ampacity, I find this hard to believe unless manufacturer instructions require it.


Not trying to get off topic but how does one get "?" symbol into the text- or better yet a list of other symbols also. I copied this one from jims post.

 

[templdl]

Did I say that the 9 0degC rated wire was applied at 90degC?
I believe that I stated that 90degC rated wire must be used but that it must be applied at 75degC which means that the 75degC terminals at rated for it.

 

[kwired]

Did I say that the 9 0degC rated wire was applied at 90degC?
I believe that I stated that 90degC rated wire must be used but that it must be applied at 75degC which means that the 75degC terminals at rated for it.

I read you correctly, my question is where is this requirement, maybe mfg instructions? Never installed a 100% device, but am not seeing this requirment in NEC. See 110.14(C) no mention of different rules for 100% devices.

 

[SG-1]

The last two lines on the nameplate are saying for 126 ampere & above you are to use 90 degree C conductors. For 125 Ampere & below 60/75 degree C conductors are acceptable.

This is not however a 100% rated OCPD.

http://forums.mikeholt.com/attachment.php?attachmentid=3989&d=1257841496

 

[jim dungar]

The last two lines on the nameplate are saying for 126 ampere & above you are to use 90 degree C conductors. For 125 Ampere & below 60/75 degree C conductors are acceptable.

This is not however a 100% rated OCPD.

http://forums.mikeholt.com/attachment.php?attachmentid=3989&d=1257841496

Having a requirement for 90?C insulation is not the same as allowing the conductors to be sized using the 90? column ampacity.

 

[jim dungar]

Not trying to get off topic but how does one get "?" symbol into the text- or better yet a list of other symbols also. I copied this one from jims post.

There are many special characters you can get by holding down the ALT key and then typing in a four digit number on a '10 keynumeric keypad' (not the number keys across the top of the keyboard)

These are ones I use often, you can find more on-line.
ALT 0176 = ?
ALT 0177 = ?
ALT 0178 = ?
ALT 0179 = ?
*

 

[mull982]

If a terminal is rated for 75deg C you can use 90deg wire and derate the wire based on the 90deg C column as long as the final derating is lower then the value listed in the 75deg C column.

 

[mivey]

These are ones I use often, you can find more on-line.

I tend to forget the sequences. I have a character map icon so I can pick what I want. The Character Map tool is in Start-> Programs-> Accessories-> System Tools. It lists the symbol for the font you select, the keystroke sequence, description, etc., and will also let you search by the description.

 

[Jraef]

Breaker mfrs must supply 100% rated breakers with 90?C lugs because you must use 90?C rated cable (sized at 75?C ratings), which usually means copper lugs. More expensive, takes longer to get. In addition, you can't just willy-nilly insert a 100% rated breaker into a panelboard, there are very specific UL enclosure sizing rules that go along with the 100% ratings, which almost universally precludes off-the-shelf panelboards. So in effect, although there are issues and applications where the 100% ratings will provide a sizing / cost benefit, it usually favors an OEM, not an installing contractor.

For what it's worth, there are some breakers available with 100% rating at trip levels below 200A and they are not solid state. The Siemens VL breakers fit that category, their DG Series is a 150AF, trips are available down to 50A.

 

[Jraef]

I tend to forget the sequences. I have a character map icon so I can pick what I want. The Character Map tool is in Start-> Programs-> Accessories-> System Tools. It lists the symbol for the font you select, the keystroke sequence, description, etc., and will also let you search by the description.

I put a Character Map shortcut in my launch Bar, it makes it quick to get to. For some reason the Alt + sequences don't work for me when typing in Reply boxes for this Forum.

 

[SG-1]

Breaker mfrs must supply 100% rated breakers with 90?C lugs because you must use 90?C rated cable (sized at 75?C ratings), which usually means copper lugs. QUOTE]


Am I correct saying that the 75 degree conductor's insulation would be damaged by the breaker's internally generated heat that is dissipated through the breaker terminals as it cools itself using the conductors ?

 

[SG-1]

Having a requirement for 90?C insulation is not the same as allowing the conductors to be sized using the 90? column ampacity.

Jim, we are in complete agreement using the 60 or 75 degree columns to size the wire.

 

[Jraef]

Am I correct saying that the 75 degree conductor's insulation would be damaged by the breaker's internally generated heat that is dissipated through the breaker terminals as it cools itself using the conductors ?

Yes. That's what it's based on.