for a tenant improvement design within a mall, if one is not able to get the available fault current at the point the tenant receives electrical service, any thoughts about the methodology for developing the fault study for the tenant panels? Is it acceptable to leave it up to the conntractor to verify the fault current or how about assuming a large value to be conservative?
fault study
- Thread starter roberts
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Re: fault study
Are you saying that the utiltiy will not provide the fault current at the transformer secondary to you? If so, that is very unusual. If you know the size of the transformer you can estimate the fault by using the following information.
secondary current = Trans KVA/(voltage kv x 1.73)
fault current = secondary curent/ %Z
example 500 kva 208 volt secondary %Z = 5%
sec current = 500/(.208 x 1.73) = 1390 amps
fault = 1390/.05 = 27800 amp.
This is much greater than what the actual fault
will be.
[ September 05, 2003, 03:14 PM: Message edited by: bob ]
Are you saying that the utiltiy will not provide the fault current at the transformer secondary to you? If so, that is very unusual. If you know the size of the transformer you can estimate the fault by using the following information.
secondary current = Trans KVA/(voltage kv x 1.73)
fault current = secondary curent/ %Z
example 500 kva 208 volt secondary %Z = 5%
sec current = 500/(.208 x 1.73) = 1390 amps
fault = 1390/.05 = 27800 amp.
This is much greater than what the actual fault
will be.
[ September 05, 2003, 03:14 PM: Message edited by: bob ]
Re: fault study
The proper method would be to get the available fault value from the Landlord. We do a lot of tenant finish work and we always try and get the right information from the landlord or his shell engineer. They are responsible for providing that data. If there is no engineer available, maybe you could offer your services (at a reasonable cost) to perform a fault current study for the landlord.
If the distribution is not too complicated then you could recreate the calculation assuming that you know the utility transformer size, service conductor, overcurrent limitation, series ratings (of any) and any other pieces that would effect the fault current.
You could assume a high number but that would not be in the best interest of your client who would like to keep cost as low as possible.
You could make the contractor responsilbe for determining the available fault current, but will he put out the effort to determine the actual value? Beside this is not his job and he is not licensed to deteremine the available fault currents. This is a part of the electrical design which means the engineer is responsible for the correct values.
Hope this helps.
The proper method would be to get the available fault value from the Landlord. We do a lot of tenant finish work and we always try and get the right information from the landlord or his shell engineer. They are responsible for providing that data. If there is no engineer available, maybe you could offer your services (at a reasonable cost) to perform a fault current study for the landlord.
If the distribution is not too complicated then you could recreate the calculation assuming that you know the utility transformer size, service conductor, overcurrent limitation, series ratings (of any) and any other pieces that would effect the fault current.
You could assume a high number but that would not be in the best interest of your client who would like to keep cost as low as possible.
You could make the contractor responsilbe for determining the available fault current, but will he put out the effort to determine the actual value? Beside this is not his job and he is not licensed to deteremine the available fault currents. This is a part of the electrical design which means the engineer is responsible for the correct values.
Hope this helps.
BAHTAH
Senior Member
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- United States
Re: fault study
Usually a call to a planner at the local utility can get you the available fault current for a new or existing service. I have two methods since I see many plans with no fault information provided either because the Engineers are not local or they are and lazy. Our local utility provides a letter with a listing of the transformers they purchase with a list of the available fault currents based on infinite primary faults being available. This provides a quick reference to determine what will most likely be available, less any motor contribution. If the service is existing you could look at the fault ratings of the breakers in the existing equipment which would give a good idea as to what was designed for at the original installation.
Usually a call to a planner at the local utility can get you the available fault current for a new or existing service. I have two methods since I see many plans with no fault information provided either because the Engineers are not local or they are and lazy. Our local utility provides a letter with a listing of the transformers they purchase with a list of the available fault currents based on infinite primary faults being available. This provides a quick reference to determine what will most likely be available, less any motor contribution. If the service is existing you could look at the fault ratings of the breakers in the existing equipment which would give a good idea as to what was designed for at the original installation.
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