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Fixed 110v installation advice

Will Elec

Hi all,

Just in the process of planning a 110v install in a small workshop.

Using a 2kva (centre tapped 55-0-55) wall mount transformer, first question is regarding the primary protection for the transformer, the primary current is around 9a but seem to be getting conflicting views regarding the appropriate MCB to feed the primary. Seem to see figures between 125% and 250% to allow for inrush - I was thinking a 20a D rated MCB should do the job but would appreciated thoughts on this!

The transformer will feed 8 (not all will be used at once - only a one person workshop) 16a commando sockets (radial). The transformer has no built in overcurrent protection on the secondary so was thinking of a small db with a double pole mcb. Even though the commando sockets are rated 16a is it suitable to use a 20a C rated mcb as it is a radial (and transformer output is around 18a)?

Thanks in advance for your input - not used to this 110v!

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  • 0

    you are right to worry about inrush. A C or D breaker wil be needed, and even then, it may be worth adding a surge limiter in series - I have done this inside the box  on a bit of ceramic choc bloc in the past..

    This sort of thing, but selecting the right one needs a bit of thought. At room temp they add some ohms and over about half a second once power is  on they heat up to offer a far lower resistance. They do need to be kept away from plastics though.

    20A breaker feeding any no of 16A sockets is fine. The hard part is finding one that senses and breaks on both poles. If you want RCD cover on the 110V side, and you may well,  then be aware that models of RCD or RCBO with built in electronics sold for 230V may not work on 110, and the self test may not pass enough current to do the needful.

    Mike

Reply
  • 0

    you are right to worry about inrush. A C or D breaker wil be needed, and even then, it may be worth adding a surge limiter in series - I have done this inside the box  on a bit of ceramic choc bloc in the past..

    This sort of thing, but selecting the right one needs a bit of thought. At room temp they add some ohms and over about half a second once power is  on they heat up to offer a far lower resistance. They do need to be kept away from plastics though.

    20A breaker feeding any no of 16A sockets is fine. The hard part is finding one that senses and breaks on both poles. If you want RCD cover on the 110V side, and you may well,  then be aware that models of RCD or RCBO with built in electronics sold for 230V may not work on 110, and the self test may not pass enough current to do the needful.

    Mike

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