Circuit Breaker Help please

Discussion in 'General Electronics Chat' started by Hurdy, Mar 28, 2006.

  1. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    Hi everyone,

    I have a question concerning circuit breakers.
    Here is my scenario.

    I have a control unit that has a 230V supply running into it and I need some kind of overload trip device.
    The 230V supply is being fed to a pump that will pull around 1.2A and a band heater that pulls around 5A.
    I need devices that will trip if too much current is being pulled by either the pump or the heater.
    I know I can use an Overload relay,1.10-1.60A FLC for protection against the pump, but I need something for the heater.
    I have been browsing a site that is linked below that can supply cheap MCBs and RCDs but I have no clue what the difference between them are.

    http://www.toolstation.com/shop/Electrical...on/d190/sd2615/

    Could someone please advise me.

    If my description isn’t enough information please let me know and I will try and amend it.

    I have also included a datasheet for the pump Overload relay,1.10-1.60A FLC I have found.
     
  2. Erin G.

    Senior Member

    Mar 3, 2005
    167
    1
    What you need is a circuit breaker from the service panel that is rated for the combined loads of the motor and heater.

    Motor overloads are usually part of the motor control circuit. They protect the motor by opening the control power circuit if the motor draws too much current for a specified period of time (usually a few seconds).

    If you were to feed your loads from a 10 amp circuit breaker, the breaker itself will protect the heater, and the motor starter/overload device will protect the motor.

    If coming strait off the circuit breaker in the service panel is not practical, then you may use a motor starter to protect the heater as well. I've found one on the web link you listed:

    http://www.toolstation.com/shop/Electrical...ies/d190/sd3080

    product number: IEC 947-3 Degree. IP65. You would just need to order thermal over loads sized for the heaters.

    Hope this helps.

    erin
     
  3. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
    An MCB is a conventional Circuit breaker, and what you want.
    An RCD is a "Residual Current Device", otherwise known as an Earth Leakage Breaker, or Core Balance Relay, designed not to trip on over current, but if there is over 30mA (or 10mA on some devices) current leakage from either phase or neutral to earth i.e., it measures the current on the phase, and compares it with the current on the neutral, and if there is more than a 30mA discrepency will trip an internal relay. They are used to protect against electrical shock, and commonly used in "Wet Area's", or on outside plugs. They have been Manditory on all switchboards to protect ALL outlets over here since 2004.
    There are also Combo units available that do both jobs.
     
  4. paultwang

    Well-Known Member

    Mar 8, 2006
    80
    0
    Also known as ground fault interrupter (GFI / GFCI)?
     
  5. PointGiven

    New Member

    Sep 10, 2005
    7
    0
    What about a fuse?
     
  6. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    Thank you for your help guys, very much appreciated.

    I have another problem. I have recently purchased a Siemens overload relay, but I dont quite understand it.
    If you look at the datasheet I have provided with this post you will see on the first page that there are two parts to this relay. I had ordered this part thinking that both pieces came together, but to my supprise it only came with the lower half.
    The datasheet shows two type of upper halfs. What does it do? Why does it not come as one? Which type of upper half do you suggest I need for my project?

    I have also been looking at MCBs. Do you recommend signle pole or double pole MCBs? or does it not matter? I take it I should purchase a 10A MCB for my incomming supply, then split it off to my overload relay and a 6A MCB to protect my 5A heater.

    Thank you,

    Rob
     
  7. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    The missing part of the Siemens device is the contactor. See chapter four of this reference: Sirius Systems Manual
     
  8. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    Hi again everyone.

    I have now got both parts to my overload relay but cannot make sense of it.

    I have all of these ports labelled L1, L2, L3, 13 NO, A1, 95 NC 96, 97 NO 98, A2, 2T1, 4T2, 6T3, 14/22 NO/NC.

    I know NO stands for normally open and NC for normally closed but this doesn't make it any easier for me.

    Basically I want a supply in of around 2A and a supply out to a motor of 2A.
    Which pins do I connect supply in to and which one to supply out.

    I have included a picture of my relay.

    Thanks,

    Rob
     
  9. Erin G.

    Senior Member

    Mar 3, 2005
    167
    1
    L1, L2 & L3 get "line power" from your source voltage. 2T1, 4T2, 6T3 go to your load, in this case your motor. When the contactor closes L1 will close to T1, L2 to T2, and L3 to T3. If you are only using 230VAC single phase, then you will only use two of the Ls and two of the Ts. In industry we usually use the outside contacts, L1 to T1 and L3 to T3. It really doesn't matter though, as long as the Ls are connected to the source, and the Ts are connected to the motor.

    A1 And A2 are the coil leads. If the coil is rated for 110VAC, then A2 would get wired up to the neutral of your control power, and A1 would be wired up to the hot through a start button or other device, such as a PLC output. A1 is usually protected by a fuse. When A1 gets it's 110VAC, then the contactor closes as described above.

    95 & 96 are auxillary contacts, normally closed: 97 & 98 are auxillary contacts, normally open. Both of these are on the overload part of the assembly (bottom). 14/22 goes through the over load and probably ties into 14 on the contactor (top part of the assembly), and 13 & 14 are aux contacts, NO on the contactor.

    Just for clarification, "normally" means when the conactor is NOT energized.

    When A1 is energized, closing the L- to T- contacts, the contacts on 95 & 96, 97 & 98, and 13 & 14 will change state as well. That means as long as the contactor coil is energized, 95 & 96 will be open, and 97 & 98 will be closed, and 13 & 14 will be closed. These contacts can be used for indicator lights, "seal-in" or holding circuits, or any other number of applications. If you don't have any plans for them, ignor them.

    Notice that when the overload (bottom) is connceted to the contactor (top), you MUST connect the neutral to the overload's A2 terminal. The overload device is sensing load on the main, or L- to T- contacts. If an overload condition occurs, the overload device will open A2 between itself and the contactor, thereby killing the 110VAC to the contactor coil. That in turn opens ALL of the contacts, returning them to their "normal" state, and hopefully saving your motor from burning up.

    Check page 2 of the PFD file you attached 2 posts ago. There is an excellent drawing of everything I've described. The dotted lines between the contacts indicate that they are mechanically interlocked, or operate together.

    Sorry this was so long, but but I hope it helps clear things up a bit.

    erin
     
  10. Hurdy

    Thread Starter Senior Member

    Feb 27, 2006
    137
    0
    Thank you Erin you have been a massive help! More than you can imagine! Very much appreciated! I will take a look at wiring it up when my cable arrive. hehe.

    Thanks again,

    Rob
     
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