MTW 600V 105°C Wire Ampacity

[Ranker]

Sizing MTW 600V 105°C wires for use in mobile generators of >100kVA and operating in ambient up to 40°C. Wires sizing in question will connect alternator to voltage selector switch and then to circuit breaker. Question is how to determine wire ampacity rating, NEC ampacity table for <2000V, single conductor in free air, 105°C insulation seems to not exist, neither Table 310.15(B)(17) or 310.15(B)(20) satisfy my installation. By using either table mentioned I will not be able to utilize the wires full potential. Could someone please advise on how to properly size MTW/TEW 600V 105°C single conductor in free air at 40°C ambient?

 

[tkb]

You are limited to the temp rating of the termination.

 

[zbang]

Is this going to be a NRTL listed package? I'm not sure that the NEC will apply then. What do the wire manufacturers say about ratings?

 

[Ranker]

Is this going to be a NRTL listed package? I'm not sure that the NEC will apply then. What do the wire manufacturers say about ratings?

No NRTL listing. Wire manufacturer ampacities are far greater than any NEC tables, this concerned me I was approaching it wrong. Defining proper regulatory body has proven to be difficult.

 

[Ranker]

You are limited to the temp rating of the termination.

Ah, UL temperature rating for lug is 90°C. So this is going to derate my 105°C wire to 90°C?

 

[kingpb]

Ah, UL temperature rating for lug is 90°C. So this is going to derate my 105°C wire to 90°C?

That is correct. The default is typically 75 deg C column, but if you have verified proof that the terminations are designed for 90 deg C than that should work.

Another issue you may be faced with is that you may be limited to 80% loading of the rated circuit breaker ampacity unless the breaker is 100% rated. The cable size would still be based on 90deg C, but how much you can put on it may be circuit breaker limited. Just depends on the manufacturer and breaker type. You should be able to find out from manufacturer.

 

[tkb]

Ah, UL temperature rating for lug is 90°C. So this is going to derate my 105°C wire to 90°C?

A lug may be 90°c but if you terminate the lug to a piece of equipment like a breaker you will be limited to 75°c or 60°c.

 

[templdl]

Trump

Trump

Is this going to be a NRTL listed package? I'm not sure that the NEC will apply then. What do the wire manufacturers say about ratings?

NTRL. or not I would like to understand that the assembly has components that are UL listed and to comply with he UL listing of the components the terminal temperature rating will trump anything else as previously stated. The 105degC provides the latitude for any derating consideration.

 

[kingpb]

A lug may be 90°c but if you terminate the lug to a piece of equipment like a breaker you will be limited to 75°c or 60°c.

In principal I would agree, however I would change one word in your comment:

"A lug may be 90°c but if you terminate the lug to a piece of equipment like a breaker you MAY be limited to 75°c or 60°c."

I will also agree that it is highly likely to be limited, but not guaranteed. One must always check if in question.

 

[don_resqcapt19]

Also note that even where you are permitted to use the free air ampacities of Table 310.15(B)(1), the terminations are limited to the ampacities in 310.15(B)(16) based on the temperature rating of the equipment that the conductors are terminated on.

 

[tkb]

In principal I would agree, however I would change one word in your comment:

"A lug may be 90°c but if you terminate the lug to a piece of equipment like a breaker you MAY be limited to 75°c or 60°c."

I will also agree that it is highly likely to be limited, but not guaranteed. One must always check if in question.

:thumbsup:

 

[Julius Right]

I agree with tkb. In NEC art. 310.15 Ampacities for Conductors Rated 0–2000 Volts. it is here a note:
Informational Note No. 2: For the allowable ampacities of Type MTW wire, see Table 13.5.1 in NFPA 79-2007, Electrical Standard for Industrial Machinery.
Actually, it is Table 12.5.1 where the maximum temperature for this type of cable it is only 75oC.
In the same NEC article 310.15 another note states:
Informational Note: See 110.14(C) for conductor temperature limitations due to termination provisions.
art.110.14(C) states (3) Conductors with higher temperature ratings if the equipment is listed and identified for use with such conductors.
In this case you may calculate the ampacity according to 310.15 (C) Engineering Supervision.
This means calculate according to IEEE 835 or directly following Neher and McGrath publication.
If it is not the case then [ briefly] for up to 100 A the conductor insulation will be 60 and for more 75oC rated.:weeping: