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Pump Start relay

Discussion in 'Irrigation' started by fall46, Aug 13, 2009.

  1. AI Inc

    AI Inc LawnSite Fanatic
    Messages: 26,629

    Boots , its absolutly georgous outside, get off this stupid thing and go enjoy your life.
  2. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,267

    How about you get bent?
  3. Dripit good

    Dripit good LawnSite Bronze Member
    Messages: 1,081

    Why would you talk to your brother like that? :nono:

    He was being nice to you.
  4. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,267

    Brothers will live longer and more happily when they forbear from telling others what to do.
  5. Kiril

    Kiril LawnSite Fanatic
    Messages: 18,334

    Boots, I fail to see your logic here.

    Considering the general rule of thumb is to only load a circuit to 80% of it's capacity, a load of 25 amps on a 30 amp circuit doesn't satisfy that rule.

    Please explain exactly why one can't put a 25 amp relay on a 30 amp circuit.
  6. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,267

    It was explained to me by a licensed electrician who looked at my obviously-made-by-a-plumber sketch for some wiring I wanted done, and informed me that electricity worked differently.

    Any component in a wiring circuit MUST be able to safely pass all the current it might happen to encounter. In a 30-amp branch circuit, the bar is set at 30 amps. Number ten wire at a minimum. 30-amp rated receptacles. A relay on this branch would have to have a 30-amp rating at a minimum. The idea is that you don't burn the house down forcing current through devices that aren't rated for it.

    Note that there is one exception to this rule, that allows 15-amp receptacles to be installed on a 20 amp circuit (provided that there is more than one receptacle on the circuit) ~ it happens that the standard of construction for 15 amp receptacles allows them to be UL-rated for 20-amp pass-through.
  7. Kiril

    Kiril LawnSite Fanatic
    Messages: 18,334

    While this makes sense, I'm not sure I agree with the logic. We are most likely talking about a dedicated branch circuit feeding a pump with a known load. As long as the relay is sized appropriately for the equipment it is powering is should be OK.

    Now if your circuit continues beyond the relay (i.e. it is being fed through the relay) then I can see why it should be rated the same as the circuits over current protection, but is this the case here?

    Say we have a pump that has no relay. If the pump has a FLA of 8 amps (~9 amps with service rating), then according to your electrician, I cannot hardwire it to a 15 amp breaker because it is not capable of handling 15 amps .... right?

    The primary items the NEC addresses with respect to pumps is over current protection (per section 430).


    Either way, downsizing the breaker to 20 amps or putting in a fusible disconnect would probably be a cheaper solution than upsizing the relay if the price is really as high as your suggesting. We are talking about a 3/4 HP pump here, 20 amps is pushing the max over current protection allowed when using the 150% multiplier and FLA from table 430.148 anyhow.

    Note, I don't have a copy of the NEC in front of me, and local codes may differ anyhow, so best to check with the city to find out what is and is not allowed.

    I don't believe this is a good comparison. A hardwired pump load and a standard plugged load are not really comparable.
  8. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,267

    The logic is, and always will be - YOU DO NOT BURN THE HOUSE DOWN. The codes are to ensure that none of the fixed wiring ever starts a fire. Codes don't care about what's plugged into a receptacle, so much as caring whether the receptacle itself, and the wiring leading up to it stays cool enough to be safe.

    By the way, the 30 amp line the OP mentioned is suspicious all by itself. How many 30 amp circuits do you ever see in homes, for 120 volts, that is. I could visualize an old fusebox, with a 30-amp glass fuse in place of the 15 or 20 that belongs there.

    Remember that the OP wants to switch the entire branch circuit with a relay, from inside the house. What any pump on that circuit may or may not do is immaterial. The relay must carry the full load that the branch circuit is capable of delivering. Plugged in? Hard-wired? Makes zero difference. Motors are capable of shorting out, or maybe even a partial short-out, drawing continuous overloads.

    By the way, one other exception may still exist, and that's for an arc-welder receptacle. Your standard Lincoln stick welder is fed from a 50-amp breaker, but you can see wiring as small as #10 feeding the receptacle. I know that the Lincoln welder can only draw an intermittent load at the highest currents, and a #10 feed won't become overheated. It could be that the arc-welder plug is not ever found on equipment that can draw a continous heavy load.
  9. Kiril

    Kiril LawnSite Fanatic
    Messages: 18,334

    Well, I'm not going to pretend to know how exactly to interpret NEC Article 430, but it doesn't seem to support what you are saying.



    Fact of the matter is, pump overload protection and branch circuit protection (Article 240) are treated separately by the NEC. Anyone attempting to install a pump should be intimately familiar with Article 430.

    Another appropriate article.

    Last edited: Aug 17, 2009
  10. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,267

    If you switch an entire branch circuit with a relay, it can't be rated for less current than the circuit breaker. Any argument about what is on the branch circuit is immaterial. Any link concerning pumps is irrelevant to switching the entire circuit with a relay at the breaker box.

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