generator cables

[nicky]

how do i size the connecting cables for a temp roll up generator. connecting cables from generator to ATS at building
Generator is 145kw building service is 400A

 

[rcwilson]

Voltage? Single-phase or three-phase?
Does portable generator have an output breaker to protect cables? If so what amp rating?

 

[nicky]

generator cables

3phase

 

[nicky]

generator cables

yes 400a breaker 3phase

 

[nicky]

generator cables

208v

 

[kingpb]

Your really under utilizing the generator by limiting it to 400A.

145kW at pf of 0.8 = 181KVA (prime rating?)
if it is prime rating then standby is approx 10% higher, so 160kW @ 0.8 = 200KVA

200KVA @ 208V, 3ph is 555A

 

[rcwilson]

145 kW generator, assume .85 power factor 145/0.85= 170 KVA

170 kVA @ 208 V 3 phase = 170 x 1000/(208*1.732) = 471A. With a 400 A breaker, the generator is probably 145 KVA, I = 145 x 1000/(208 x 1.732) = 402 Amps.

Size cable for 400 Amps.

If it is in free air, no conduit, 75 C cable in 40C ambient, 400 kcmil copper would work per Table 310.15 (B) (20).

If it is in conduit, Table 310.15 (B)(16) applies, then 600 kcmil is required.

 

[kingpb]

145 kW generator, assume .85 power factor 145/0.85= 170 KVA

170 kVA @ 208 V 3 phase = 170 x 1000/(208*1.732) = 471A. With a 400 A breaker, the generator is probably 145 KVA, I = 145 x 1000/(208 x 1.732) = 402 Amps.

Size cable for 400 Amps.

If it is in free air, no conduit, 75 C cable in 40C ambient, 400 kcmil copper would work per Table 310.15 (B) (20).

If it is in conduit, Table 310.15 (B)(16) applies, then 600 kcmil is required.

Those are some reasonable assumptions given the limited info, but keep in mind a standard PF for most engine generators is 0.8. Also, typically, the rating most people talk about is the prime rating, again, which most engine generators will have standby rating which is 10% greater.

Regardless, if the service it is feeding has a 400A main breaker, then it really doesn't matter what the gen rating is above that, and I agree all you need is 400A worth of cable.

 

[nicky]

generator cables

they are free air
what about if they are single cables ea leg - can't they be smaller

 

[socalelect]

when you say roll up genny are you meaning its on a trailer and not a permanet resident ?

we have a couple gennys set up for this they are MQ's even thoe brand dosent matter ours have camlock connectors
some gennys dont most have bus's for bolt down lugs
i believe we run 4/0 SC cable with cam locks i was told the cable was good for 400 amps but i have personally not done the math
there is a company out there that makes really cool generator docking boxes that have camlocks or bolt down bus's i have installed a few but cant remember the manufacture

so if its a portable unit you may be able to go the SC cable route

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheetOEM146 link with specs for the sc cable

 

[nicky]

generator cables

yes a roll up on trailer with a gen connect box
cam locks from generator to agen connection box permantly installed at site
that is what I was thinking size wise
was not sure on sizing

 

[socalelect]

yes a roll up on trailer with a gen connect box
cam locks from generator to agen connection box permantly installed at site
that is what I was thinking size wise
was not sure on sizing

check out table 400.6 (B) i believe if you end up using single cable make sure you can secure them somehow , a few of ours have some how grown arms and disconnected themselves they grew legs and ran off 　

 

[nicky]

generator cables

thanks

 

[maghazadeh]

so if its a portable unit you may be able to go the SC cable route

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheetOEM146 link with specs for the sc cable

So base on South Wire, their 4/O SC cable is good for 405 AMP, But no one here mentioned consideration for voltage drop if distance is great.
This kind of install will be under temporary category which there is a limitation for time.
Last time I dealt with such situation, local AHJ did not allow installation for longer than 3 days at the time. They said such temporary installation is there for special events like concert, but not for using as stand by for computer / server rooms.
In other word, they would give permit for 3 days, then you had to move the trailer some distance and bring it back with application for another permit.
Has anyone went through this before?

 

[Smart $]

So base on South Wire, their 4/O SC cable is good for 405 AMP, But no one here mentioned consideration for voltage drop if distance is great.
This kind of install will be under temporary category which there is a limitation for time.
Last time I dealt with such situation, local AHJ did not allow installation for longer than 3 days at the time. They said such temporary installation is there for special events like concert, but not for using as stand by for computer / server rooms.
In other word, they would give permit for 3 days, then you had to move the trailer some distance and bring it back with application for another permit.
Has anyone went through this before?

Typically the minimum size is determined by termination temperature limitations of 110.14(C)

 

[socalelect]

So base on South Wire, their 4/O SC cable is good for 405 AMP, But no one here mentioned consideration for voltage drop if distance is great.
This kind of install will be under temporary category which there is a limitation for time.
Last time I dealt with such situation, local AHJ did not allow installation for longer than 3 days at the time. They said such temporary installation is there for special events like concert, but not for using as stand by for computer / server rooms.
In other word, they would give permit for 3 days, then you had to move the trailer some distance and bring it back with application for another permit.
Has anyone went through this before?

we have a set up very similar to the op's at one of our buildings , man. xfer switch with a generator dock box we use cables with camlocks that are approx 15 feet long . the gen isnt hooked up all the time thoe . we also have a couple customers that have that set up and will rent gennys and have us tie them in in that manner , our ahj hasnt raised a eyebrow yet...... just wait till they get bored