for switch why is motor amp rating of 24, lower than 30 amp rating?

Discussion in 'General Electronics Chat' started by sdowney717, Dec 12, 2014.

  1. sdowney717

    Thread Starter Member

    Jul 18, 2012
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  2. Papabravo

    Expert

    Feb 24, 2006
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  3. MaxHeadRoom

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    Jul 18, 2013
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    Yes it could be load dependent, AC/DC? inductive/resistive? Duty cycle?
    Max.
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
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    rated 24 amps inductive (motor) load, 30 amps resistive. inductive loads have spikes and surges that resistive loads dont have.
     
  5. crutschow

    Expert

    Mar 14, 2008
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    The relay motor rating is for the steady-state operating motor current. It's been derated to handle the large starting current that motors typically generate.
     
  6. sdowney717

    Thread Starter Member

    Jul 18, 2012
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    I am planning on using such switch for AC 120v, a variety of loads, mostly resistive ones.
    It will be backed up from source power with a 30 amp mains breaker. It will be on 100% of the time. It would only ever turn off IF I sail to another marine with a true twin 30 amp power post on the dock.

    Idea is on the boat when plugged into shore power. The boat has twin 30 amp inlets, separate hot, neutral and ground which splits up various AC loads.
    I could run another shore power cord, but it is going into the same little outlet next to the boat slip. The outlet is fed by a 30 amp breaker. I supposedly have to share with the slip next to me, he is not there for a few months. Anyway half my AC system is always disconnected. (2 cabin heaters, water heater), I basically can never use.

    My idea is wire in the 2 pole switch to merge my twin 30 amp boat AC circuits into one. This way I can run it all from the one shore power cord. The boat has twin 30 amp AC breakers on the mains in the boat, so if I suck to much current, that breaker will trip. I have a separate mains breaker box with the two breakers, a relay switching control box that selects between shore-gen-inverter power and circuit breaker panel with spots for 8 distribution breakers.

    So I know it is not ideal, but If careful not to turn on everything at once I can run more than I can now.
     
  7. MaxHeadRoom

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    Jul 18, 2013
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    If the 30a breaker is feeding dual outlets, you should check whether each are on the same 120v line, often adjacent sockets are on each 120v line of the 240v pair in order to balance the load.
    If so, you would have 240v between each live conductor, if you merged them, it would obviously blow the breaker.
    Max.
     
  8. sdowney717

    Thread Starter Member

    Jul 18, 2012
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    Sure would blow the breaker! If I hooked up to a 50 amp 240v ac line, or maybe a 120v 30 amp plugs on different phases.
    Breakers are nice things to have. As long as the switch can handle the current, and it will be closed all the time really.
    The marina I am at is not very sophisticated, there is no multi phase on any single post. This marina was built in 1948, and the wire is old standard white romex 12 gauge.
    Occasionally with high tides in storms the post with plug will go underwater.
    Hey it is free power, so I can't complain. Some boat owners have had their own power meters installed and pay monthly.
     
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