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Circuit Question

  • 01-07-2010 4:08pm
    #1
    NoseyMike2010
    Registered Users, Registered Users 2 Posts: 420 ✭✭


    Attached is a copy of a circuit that I believe is hooked up onto mains and also a PSU.

    I have a few questions I am wondering

    1) Why is 120VAC and 24VDC both needed? Why do you need one supply to be AC and one supply to be DC. Is this the case for all circuits. I am guessing that one will act as backup.

    2) DOes the isolator shut down the circuit. Ir if the isolator is shut does that mean the other power supply works instead.

    3) What is the MCB doing?


Comments

  • #2
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    i assume it's USA 120v from a ups feeding a 24v power supply

    the mcb seems to be protecting the PS

    if it's the usa split-phase 240v and they're using '1 hot leg' and neutral for 120v- i'm not clear why they're using a 2-pole mcb?


  • #3
    studdlymurphy
    Registered Users, Registered Users 2 Posts: 832 ✭✭✭studdlymurphy


    As posted above. The 120v is a UPS (Uninteruptable power supply- Normally with battery backup) US mains supply. This supply is then used to give power to a 24vdc power supply. The MCB is a 6A fuse to protect the 24vdc power supply.


  • #4
    NoseyMike2010
    Registered Users, Registered Users 2 Posts: 420 ✭✭NoseyMike2010


    Would I be correct to say that if the 120V became disconnected or unavailable that the 24V PSU would power the circuit.

    How did you guys know that the MCB is 6A? How did you calculate it from that drawing?


  • #5
    Doolittle51
    Registered Users, Registered Users 2 Posts: 417 ✭✭Doolittle51


    NoseyMike2010 wrote: »
    Would I be correct to say that if the 120V became disconnected or unavailable that the 24V PSU would power the circuit.

    No. The 24VDC Power Supply is powered from the 120V AC supply. It's a very basic circuit.
    NoseyMike2010 wrote: »
    How did you guys know that the MCB is 6A? How did you calculate it from that drawing?

    It says MCB 6A


  • #6
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,641 Mod ✭✭✭✭2011


    M cebee wrote: »
    i assume it's USA 120v from a ups feeding a 24v power supply

    the mcb seems to be protecting the PS

    if it's the usa split-phase 240v and they're using '1 hot leg' and neutral for 120v- i'm not clear why they're using a 2-pole mcb?
    +1

    There are a number of reasons that DP MCBs are used. For example when mains voltage (including 120 VAC) to supply a device in an ATEX zoned area ET-105 states that DP MCBs must be used.


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