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Thread: SPD to protect GFCIs

  1. #1
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    SPD to protect GFCIs

    To vendors, electricians, engineers,

    For a house with 10 GFCI receptacles, they would be useless if the GFCIs got fried by external surges. The internal MOV (Metal Oxide Varistors) in each is not enough. They are good for only a few years then the GFCI circuit become vulnerable to damage.

    Now consider this Siemens whole house 140,000A surge current SPD (Surge Protector Device) with data sheet at:

    https://www.downloads.siemens.com/do...id1=BTLV_43434

    available at amazon https://www.amazon.com/gp/product/B0...k_ql_qh_dp_hza





    The wires are only size #10 AWG and it requires 20A breaker.

    What would happen if this is connected to the main breaker of say 100A instead of buying 16 pieces and connecting to each 20A breaker.

    Note it is not an appliance. It doesn't conduct at normal voltage. Only when it reaches above the threshold voltage (MCOV rating) that it begins to conduct and do the voltage divider impedance action thing. But notice that this voltage divider action is only for the surges, not the normal 100A current.

    So my question is whether Siemens requiring it to put on each 20A breaker and buy 16 pieces is just sales gimmick instead of buying just one to put on the main 100A breaker.

    Can the 100A regular current really passes through the Siemens SPD when the SPD only conducts at higher voltage during actual surges. Even then, the voltage divider action is for only for the surge current and not the regular 100A, is it?

    Btw.. let's not confuse the 140,000A surge current rating which is the capacity of the Surge current the SPD can handle, not the regular current (note too that Siemens knows their #10 awg can handle 140,000A surge current because it is not continuous.. so what's wrong putting it in 100A breaker instead of buying 16 pieces for each 20A breakers?).

    If you want to protect all the 10 GFCI receptacles at the house, what kind of main breaker SPD do you usually use? Do you really need the SPD to have #2 AWG wire. Notice an SPD is not normal load or appliance so why does the wiring have to match the regular wiring and ampere table?
    Last edited by tersh; 01-09-19 at 08:33 PM.

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    Quote Originally Posted by tersh View Post
    What would happen if this is connected to the main breaker of say 100A instead of buying 16 pieces and connecting to each 20A breaker.
    You're only supposed to add one 2p breaker to the panel that supplies only the SPD and it protects every circuit in the panel.
    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
    You're only supposed to add one 2p breaker to the panel that supplies only the SPD and it protects every circuit in the panel.
    I know. I was asking what if the 2p breaker is the 100A main breaker instead of a branch only. Putting it in the main breaker can protect the entire house. If you put it in each branch, it should only protect the circuits connected to that breaker branch only (edit: unless you mean by connecting it to one branch breaker (say 20A) only, it can protect the other 15 breakers too??)

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    Quote Originally Posted by tersh View Post
    Putting it in the main breaker can protect the entire house. If you put it in each branch, it should only protect the circuits connected to that breaker branch only (edit: unless you mean by connecting it to one branch breaker (say 20A) only, it can protect the other 15 breakers too??)
    Not correct. Even on its own breaker, it protects all circuits. It's not supposed to be connected to an existing breaker that supplies other wires.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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    The OP has a serious misunderstanding of the fundamentals of surge protection. Not only will it not make any difference if it is connected to a branch breaker or the main breaker, it would also violate the listing as it says it must be connected to a 20 amp OCPD.

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    Quote Originally Posted by LarryFine View Post
    Not correct. Even on its own breaker, it protects all circuits. It's not supposed to be connected to an existing breaker that supplies other wires.

    I added the edit a few seconds later in message 2. So by connecting it to one branch breaker (say 20A) only, it can protect the other 15 breakers too and their circuits or all loads in the entire house??

    Never realized this before although I owned another Siemens Whole House 140,000A SPD and put it in another building.

    I'll share this info to millions of households in my country, so I guess I make amazon a million dollar richer, lol. Thanks.

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    Quote Originally Posted by LarryFine View Post
    Not correct. Even on its own breaker, it protects all circuits. It's not supposed to be connected to an existing breaker that supplies other wires.
    If it's connected to an existing 30A breaker that supplies other wires and load, and the ampere of the load is only 10A or less, the Siemens connected to it would still protect the load in that shared breaker.. isn't it?

    No problem reserving a dedicated breaker to it. I thought the past 6 months it only protects the breaker it is connected too.

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    Quote Originally Posted by tersh View Post
    So by connecting it to one branch breaker (say 20A) only, it can protect the other 15 breakers too and their circuits or all loads in the entire house??
    Yes, but you should use an additional 20a 2p breaker, not one already in use supplying a load.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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    Quote Originally Posted by tersh View Post
    If it's connected to an existing 30A breaker that supplies other wires and load, and the ampere of the load is only 10A or less, the Siemens connected to it would still protect the load in that shared breaker.. isn't it?
    Not exactly; it shouldn't share a breaker. The SPD doesn't draw 20a, that's just the size breaker that should be used.

    No problem reserving a dedicated breaker to it. I thought the past 6 months it only protects the breaker it is connected too.
    Nope, all of them. Parallel is parallel.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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    This is to be used on a grounded system with a neutral conductor at the panel where it is used, not just earthed.
    Tom
    TBLO

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