tryinghard
Senior Member
- Location
- California
What is the simplest way to explain to a non-electrician that service entrance conductors have overload protection but no short circuit or ground fault protection?
Service Entrance Protection & 230.70
- Thread starter tryinghard
- Start date
- Status
stickboy1375
Senior Member
- Location
- Litchfield, CT
tryinghard said:
The SEC's are protected from being overloaded, just not protected if you used a hacksaw on them... :grin:
tryinghard
Senior Member
- Location
- California
stickboy1375 said:
Your quick :roll: :grin:
How can I explain why the OL's won't provide adequate OCP protection in this situation?
Last edited:
resistance
Senior Member
- Location
- WA
????????:-?tryinghard said:
pbeasley
Senior Member
- Location
- Orange County, CA (for now)
I find that many people can grasp water and plumbing concepts easier than electrical concepts (insert gratuitous plumber joke here) so you might try phrasing in those terms...tryinghard said:
Maybe something along the lines of: A garden hose can only give them so much water out the end, and the water company makes sure the water is available to do so, but if you punch a hole in the hose more than the garden is going to get wet.
charlie
Senior Member
- Location
- Indianapolis
I looked at this question with the idea of explaining it to my wife. That is why I haven't answered. 
:smile:
:smile:
tryinghard
Senior Member
- Location
- California
I can see the definition of ground-fault protection and I can try to explain this to others but most often they will still think the OL protection will provide the ground fault protection as well.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Why would a non-electrician know enough about short circuit and ground fault protection to bother asking the question? Why would one need to know an answer that can be understood by a non-electrician? Could you get by by simply saying the NEC does not govern the utility side of the power system? Would it help to say that if a building's SEC's were cut by a backhoe or something, and if they were destroyed thereby, the utility will still want to be able to supply power to all of the neighboring buildings?
stickboy1375
Senior Member
- Location
- Litchfield, CT
charlie said:I looked at this question with the idea of explaining it to my wife. That is why I haven't answered.
God that was funny....
tryinghard
Senior Member
- Location
- California
I work for a municipal and this municipal has many dwellings and non-dwellings with service entrance extending far into the structures both underground and surface. Commonly they installed a meter base only outside then continue serving inside 10-80', these were installed without inspections.
Often the utility linemen will make the comment "the transformer fuses will protect the service entrance, so why do you want to install a service disconnect?" and "If a fault occurs the amperes will rise extremely fast and blow the fuses at the utility transformer." The linemen don't mind having this responsibility and if anything they are bothered an electrician is even wanting to change these to include service disconnects, regardless if it is NEC or not.
I think it's actually myself that can use the help, because if I can better understand how the short-circuit & ground-fault protection will enable more efficient protection than the OL's, I will be able to explain this better to others. I do know the OL's are sized for different reasons, but if the utility does no care about convenience or customer service how is a service entrance any less protected for shorts and faults by using the OL's only?
I would like to add please do remain on topic with the question, in other words how is short circuit ground fault not provided with the serving XFMR fuses and what's the difference with or without? I do not wish to muddle with other issues please
Often the utility linemen will make the comment "the transformer fuses will protect the service entrance, so why do you want to install a service disconnect?" and "If a fault occurs the amperes will rise extremely fast and blow the fuses at the utility transformer." The linemen don't mind having this responsibility and if anything they are bothered an electrician is even wanting to change these to include service disconnects, regardless if it is NEC or not.
I think it's actually myself that can use the help, because if I can better understand how the short-circuit & ground-fault protection will enable more efficient protection than the OL's, I will be able to explain this better to others. I do know the OL's are sized for different reasons, but if the utility does no care about convenience or customer service how is a service entrance any less protected for shorts and faults by using the OL's only?
I would like to add please do remain on topic with the question, in other words how is short circuit ground fault not provided with the serving XFMR fuses and what's the difference with or without? I do not wish to muddle with other issues please
Last edited:
charlie
Senior Member
- Location
- Indianapolis
OK, now you are asking a question that we can answer since the people you are talking to have some modicum of understanding.tryinghard said:
Let these people know that most electric utilities are not concerned about protecting their transformers as much as keeping their customers in service. Since you work for a municipal electrical company, you must start on the electrical side first to see how they actually provide their primary protection. Make sure their standards engineer is aware of why you are interested.tryinghard said:
You will never convince a lineman that he is wrong since most electric utility people (not just linemen) do not understand either what the NEC has in it or why those rules are there. You will be able to talk to the standards engineer and to reason with him or her. After discussing your problem with him, he should have some clout to help with getting better installations.
I assure you that what you are attempting to do will be difficult at best and you may be out of work at worst. Good luck.
tryinghard
Senior Member
- Location
- California
Thanks Charlie, let me take a stab at this for critique:
The function of the fuses at a serving transformer is to provide transformer protection from overloading, the fuses are overload protection. Often the serving transformer will be sized to handle multiple drops, the OL's may open in a short circuit or ground fault but they are not sized or installed for this specific purpose.
The service entrance conductors require a specifically sized overcurrent protection device, it is the service disconnect and it also allows the electrical to the building to be shut off in the event of an emergency or maintenance situation. This OCP is usually a breaker and its function is to provide ground fault and short circuit protection, minimally at or near its ampere rating. These are the reasons NEC requires the service disconnect and its placement at a readily accessible location and also nearest the point of entry of the service conductors when installed indoors.
The function of the fuses at a serving transformer is to provide transformer protection from overloading, the fuses are overload protection. Often the serving transformer will be sized to handle multiple drops, the OL's may open in a short circuit or ground fault but they are not sized or installed for this specific purpose.
The service entrance conductors require a specifically sized overcurrent protection device, it is the service disconnect and it also allows the electrical to the building to be shut off in the event of an emergency or maintenance situation. This OCP is usually a breaker and its function is to provide ground fault and short circuit protection, minimally at or near its ampere rating. These are the reasons NEC requires the service disconnect and its placement at a readily accessible location and also nearest the point of entry of the service conductors when installed indoors.
- Status