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Thread: What is a service disconnect?

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    What is a service disconnect?

    I will be getting with the utility engineer myself later, but I am fairly certain that they & the city will want fused disconnect at the utility pole before it changes to underground. Thanks
    Now, again, I am a newbie to the codes and trying to learn from those more experienced than I, but, correct me please:
    If you have a meter on a pole, just a meter, mind you, and no disconnect into an underground conduit system for a normal home, or even most businesses, there are no fuses to regulate anything until you get to the main panel, where your service disconnect is. This is allowed to be derated, etc and so forth.

    There are arguments that a firemans disconnect may be needed, but nothing concrete in most places at this time.

    Above there was an argument that if a simple disconnect is used, non-fused, that this would not affect the service rating of the underground feed. This is similar to what has been used forever in Rural Farms and in many apartment complexes, where a pole mounted disconnect that is accessible only by fire poles and utility poles can reach it to disconnect the services at the top of the pole.
    Why then would they require it to be fused? Because it is 600 amps rather than 400 or 200 or 100 amps? Just trying to understand not start more fuss... Because I really cannot see the difference here. Personally, would prefer to see a definition in the code to keep it as service until it hits main disconnect at panel, and keep any firefighter or other service related disconnects as service only but having trouble seeing why there is such a difference, or, is it that we are going to be seeing a future shift from three wire service entrance to a four wire service entrance with no derating and they are trying to do it step by step?
    Last edited by ActionDave; 10-11-18 at 11:05 AM.
    Student of electrical codes. Please Take others advice first.

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    Adamjamma

    A lot of the items posted here are according to local codes. The AHJ (authority having jurisdiction) whether it be the utility company and/or the local government that inspects it. That is another reason why this is "so much fun", trying to find out what each one wants and in some cases where both of them want different things on the same job.

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    Quote Originally Posted by Adamjamma View Post
    Now, again, I am a newbie to the codes and trying to learn from those more experienced than I, but, correct me please:
    If you have a meter on a pole, just a meter, mind you, and no disconnect into an underground conduit system for a normal home, or even most businesses, there are no fuses to regulate anything until you get to the main panel, where your service disconnect is. This is allowed to be derated, etc and so forth.

    There are arguments that a firemans disconnect may be needed, but nothing concrete in most places at this time.

    Above there was an argument that if a simple disconnect is used, non-fused, that this would not affect the service rating of the underground feed. This is similar to what has been used forever in Rural Farms and in many apartment complexes, where a pole mounted disconnect that is accessible only by fire poles and utility poles can reach it to disconnect the services at the top of the pole.
    Why then would they require it to be fused? Because it is 600 amps rather than 400 or 200 or 100 amps? Just trying to understand not start more fuss... Because I really cannot see the difference here. Personally, would prefer to see a definition in the code to keep it as service until it hits main disconnect at panel, and keep any firefighter or other service related disconnects as service only but having trouble seeing why there is such a difference, or, is it that we are going to be seeing a future shift from three wire service entrance to a four wire service entrance with no derating and they are trying to do it step by step?
    A means of disconnect must be provided at or near the closest point of entry to a structure.

    Service Conductors are very limited to the length they can travel inside a structure once they get to the structure they are servicing.

    Thus you generally see a Meter/Main or Fused Disconnect, Enclosed Circuit Breaker outside by a meter mounted on a house. or a Main Breaker in the panel directly behind the meter.

    This, most times serves the purpose of both a disconnect and a means of overcurrent protection.

    That 1st means of overcurrent protection is the determining point as to where the service conductors end and where a feeder begins.

    If no overcurrent protection exists in the disconnect then the conductors passing through that disconnect from the utility are still Service Conductors.

    If there is overcurrent protection in the disconnect, such as fuses, or if the Disconnect happens to be an Enclosed Circuit Breaker then the conductors on the line side of that disconnect are Service Conductors and the conductors on the load side of the overcurrent protections device are considered a feeder.

    The rules of installation are different for Service Conductors versus Feeder Conductors.

    A Service Rated disconnect has a Neutral terminal in it and a means to bond the neutral to the Grounding Electrode Conductor inside the disconnect.

    Once that bond is made, the Grounded Conductor and the Equipment Grounding conductor must be kept separated from that point on. Thus a 4 wire feeder would be required.

    The fuses, If installed out at the pole in a fused disconnect, are not there to "de rate" the service, they are there to protect the feeder conductors to the structure because an overcurrent protection device was installed making it such.

    The decision to place the Overcurrent protection device remote from the structure is what brought the 4 wire feeder into affect.

    The NEC is not trying to shift services from 3 wire to 4 wire at all.

    The placement of the first means of overcurrent protection and where the first bond from the Grounded Conductor to the Grounding Electrode Conductor on the Customers side is what determines what type of installation you will end up with.

    This is just a very non technical overview as if we were sitting on the tailgate trying to hammer this out.

    JAP>

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    Quote Originally Posted by jap View Post
    That 1st means of overcurrent protection is the determining point as to where the service conductors end and where a feeder begins.

    If no overcurrent protection exists in the disconnect then the conductors passing through that disconnect from the utility are still Service Conductors.

    If there is overcurrent protection in the disconnect, such as fuses, or if the Disconnect happens to be an Enclosed Circuit Breaker then the conductors on the line side of that disconnect are Service Conductors and the conductors on the load side of the overcurrent protections device are considered a feeder.

    The rules of installation are different for Service Conductors versus Feeder Conductors.

    A Service Rated disconnect has a Neutral terminal in it and a means to bond the neutral to the Grounding Electrode Conductor inside the disconnect.

    Once that bond is made, the Grounded Conductor and the Equipment Grounding conductor must be kept separated from that point on. Thus a 4 wire feeder would be required.

    The fuses, If installed out at the pole in a fused disconnect, are not there to "de rate" the service, they are there to protect the feeder conductors to the structure because an overcurrent protection device was installed making it such.

    The decision to place the Overcurrent protection device remote from the structure is what brought the 4 wire feeder into affect.

    The NEC is not trying to shift services from 3 wire to 4 wire at all.

    The placement of the first means of overcurrent protection and where the first bond from the Grounded Conductor to the Grounding Electrode Conductor on the Customers side is what determines what type of installation you will end up with.
    Is it possible to have such a pole-mounted disco/OCP and still have a 3-wire supply and land on a second disco/OCP at the house?
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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    Quote Originally Posted by LarryFine View Post
    Is it possible to have such a pole-mounted disco/OCP and still have a 3-wire supply and land on a second disco/OCP at the house?
    You already know the answer to that.

    We've been through all of this before in another thread.

    The OP mentioned he didn't want to make a fuss out of all this.

    JAP>

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    Quote Originally Posted by jap View Post
    You already know the answer to that.

    We've been through all of this before in another thread.
    I honestly don't remember, but I have no dog in this fight.

    I'm simply asking whether the rule is that the first disco is the service disco, or the one on the structure being served.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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    A few points:

    1. Depends where the service point is. If there is something on the utility side, it's not a service disconnect.

    2. Note meter disconnect switches are allowed per nec. It's not really clear how/when to differentiate this from a service disconnect.

    3. Note the service disconect and OCPD must be the same or immediately adjacent to each other.

    4. Nothing wrong (per nec) with hitting a meter only on a pedestal and running hundreds of feet after.

    5. You need a fused disconnect for a meter disconnect if the fault current is above 10ka. Otherwise nonfused is fine.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    perhaps that is what I am having problems with, especially when trying to figure out the so called fireman switches. One of your statements was if a service disconnect is used an ocpd must be used almost immediately. But that then means you must upsize the rest of the wire and switch to a four wire system. No more de rating the feed.

    Perhaps this is why so many manufacturers and others are against the fireman switch. Because it takes cost up in wires so how are you going to argue it to a consumer who is looking at the idea that one: it has never been needed before, and Two, their money is already stretched to the breaking point and it just seems to be something not really needed because it hopefully will never be used.

    This gets worse when trying to figure out how to do a fireman switch for solar or other supplies in a home, where you then start looking at relays or external conduits before bringing the power inside the home. About the only way I can figure is to use a group of relays on one disconnect, so you do nut run into the six disconnect rule as well.

    Just wondering if either the rules need clarified or a whole section needs written so the fireman switches can be put into place without costing homeowners a fortune in such a way that they decide to hire handymen to wire their homes because electricians have to follow expensive rules. Personally, I do not see the need to have to switch the feeders from a fireman switch to a four wire system just because we are trying to allow firemen a way to cut power to a building before they enter it, especially when utility power can be cut by simply pulling the meter, thus the main power systems we are trying to group with the fireman main utility switch are those that supply alternate energy modes to the property.

    But again, I am a student, looking at this as if I am trying to convince a person they should add this switching system to their property for safety sake in case of fire, when no one else in a neighborhood has it on their homes, which were built earlier. It is like selling people on surge protection devices...

    Does not make it any easier when it looks in catalogues like such a switch is between 500 and 1000 dollars yet the main breaker panel can be bought for less than two hundred...
    Student of electrical codes. Please Take others advice first.

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    Quote Originally Posted by Adamjamma View Post
    trying to figure out the so called fireman switches.

    No more de rating the feed.

    many manufacturers and others are against the fireman switch.

    Just wondering if either the rules need clarified or a whole section needs written so the fireman switches can be put into place without costing homeowners a fortune in such a way that they decide to hire handymen to wire their homes because electricians have to follow expensive rules.

    Personally, I do not see the need to have to switch the feeders from a fireman switch to a four wire system just because we are trying to allow firemen a way to cut power to a building before they enter it, especially when utility power can be cut by simply pulling the meter, thus the main power systems we are trying to group with the fireman main utility switch are those that supply alternate energy modes to the property.

    I'm not sure what your meaning when you refer to "De rating the Feed" ?

    What are you considering a "Firemans Switch" and why are you so much against it ?

    I've never seen a manufacturer that was against selling product.

    The owner cannot hire a "Handy Man" that is not licensed as an electrician to do the install.

    If your local authority requires the Service Disconnect to be located on the outside of a structure, like ours does, You either put it in or your project doesn't pass inspection to get the power turned on at all.

    The utility meter does not meet the definition of a disconnect and cannot be used as one.

    The NEC does not need to be re-written.

    It would be better to take the necessary steps needed to obtain a better understanding of it.

    JAP>

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    It is more a question of why am I considering a firemans switch. The requirement for the neutral and four wire feeds and full ratings are fairly new in some ways. Well, guess it may go back to 90's but... residences were able to run 200 amp services on cables capable of running less than 200 amps from the meter to the main panel inside, whether overhead or underground. Suddenly, if a disconnect goes in between the meter and the main panel, so it can be turned off from outside the home, or from near the road on a long run like in the rural areas or places like I deal with in Jamaica, where the POCO wants meters visible from property line so they do not have to enter the property, the wiring from that disconnect must be four wire now. and at fill amps not the reduced amps. Which can add a lot more cost, especially when one adds in voltage drop. I have dealt with a property before where the customer had a meter at the driveway entrance from the road, with a disconnect on their post, and then had a half mile run along the driveway to a post in the center of their yard before splitting to feed 4 separate buildings, each treated as a main panel. To me a typical farm system. Disconnect at the meter post and disconnect at the central post in the main yard could both be used to disconnect the utility from the buildings in case of a fire. All of it run on three wires from the meter until you got to the buildings, with two disconnects that had no fuses in them. System at least thirty years old when I last saw it and worked fine.

    To do a similar system would require heavier wire and a four wire system from what many are saying... between voltage drop and the requirement now to, at least from what I am reading, create a grounded and bonded system from the meter location along the half mile driveway to the buildings.. four wire from road to buildings as well. But is it actually any safer? Or is it just adding cost? The main reason for the disconnects at the road to the main post was so if a storm blew a tree down that took the wires down, one could disconnect the power, fix the wire, and turn the power back on. Main reason for disconnect at pole in yard was so one could change services at the various buildings or even add extra buildings to the services.

    Of Course, now some farms have major three phase services supplying milk systems etc, but, most farms in Jamaica are not so advanced and with customs fees at the wharf may never get that advanced. However, fire department in Jamaica has asked if in future codes it could somehow be written to require a disconnect on the outside of all structures. Placed at no higher than 2.7 meters from either grade or sidewalk or pavement.
    Student of electrical codes. Please Take others advice first.

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