delectric123
Senior Member
- Location
- South Dakota
I have a used 45 kW 208/120v 3 ph. generator. With a 0.8 PF, whats the proper way to calculate the size fuses I need in the safety switch.
I have a used 45 kW 208/120v 3 ph. generator. With a 0.8 PF, whats the proper way to calculate the size fuses I need in the safety switch.
Are you trying to protect the generator or wire? Keep in mind the it is questionable whether or not the genset has the capacity to put out enough current for a long enough period of time or be able to develop enough fault current to blow a fuse as that which can be provided by a utility.
I also got about 125 amps. though was not sure if i used the correct formula to figure it out. could you tell me the calculations you used?
The generator has a rating of 56.25 KVA. Should i use that for sizing the OCPD?
I have a used 45 kW 208/120v 3 ph. generator. With a 0.8 PF, whats the proper way to calculate the size fuses I need in the safety switch.
Are you trying to protect the generator or wire? ...
The generator has a rating of 56.25 KVA. ...
the safety switch will be mounted on the generator. so it will also protect the conductors going to the breaker panel.
so 56250 / 1.732 / 208 = 156 amps. so i could use 150 amp fuses. but would have to downsize to 125 amp fuses to feed a 125 amp breaker panel due to the 125% rule.
... no the generator does not have a CB, just a 15 amp for control. it looks like about 20 years old
Highly recommend: Don't call it an emergency - that brings in another whole list of regulations.This generator is for emergency standby for a hog barn. what i meant by the 125% rule is, conductors feeding a breaker panel must be sized 125% for the continuos load. lets say, for a 125 amp breaker panel. 125 x 1.25 = 156.25, so the generator is perfectly sized for that. ( 56250\208\1.73 = 156)
it really isn't 125 amps continuous, i just used that for a good safety figure.Despite being a southerner, I have had little experience with a hog farm, but I ask, what makes the load continuous ?
The generator has a rating of 56.25 KVA. Should i use that for sizing the OCPD?
which breaker?
Generally speaking, it isn't worth engineering a protective system. I would recommend going with the protections already designed and installed. Be good to see what the Book says.It appears that fuses are not likely to work to well if your intent is to use fuses. Fuses do limit your options and will the generator have the capability to generated enough power to blow a fuse or trip a breaker for that matter? Should you elect to use a breaker at least you can add a shunt trip which would have the capability of opening the breaker from and external oil pressure sensor, speed sensor or another sensor than would be in tune more directly with an overload.