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staffok

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Can anyone give a simple definition of on load and off load switching? Examples of each would be great, Am i right in thinking an emergency stop is a on load and a isolater a off load.
Thanks in advance.
 
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AMST09

  • Thread Starter Thread Starter
  • #2
A light switch is an on load device as it has current going through it when you break the circuit (also MCBs)
A main switch is an off load device as there is no current going through it when the circuit is broken
 

sparks1234

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Arms
In other words you have switched off the load via the load switch before you turn the isolator etc etc, if any of you guys (and gals) use Merlin Gerin boards, the MCB switch should be turned off when the load has been removed.
 

ExArmy

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Arms
still struggling to understand the difference here, can anybody give me some more examples of the two different types please?
 

telectrix

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Mentor
Arms
Esteemed
Can anyone give a simple definition of on load and off load switching? Examples of each would be great, Am i right in thinking an emergency stop is a on load and a isolater a off load.
Thanks in advance.
yes. you are right. isolators are usually switched with no load, however, who turns off all the MCBs in a CU before turning the main isolatgor on. it'sa bit of an overlap between the 2.
 
J

Jabbajaws

  • Thread Starter Thread Starter
  • #6
So l am doing something right then. I regularly turn off MCBs before turning off the main switch. It's a practice ive followed because of something my tutor told me regarding sparks appearing at the main switch, if you don't.

However due to nerves on my Level 3, l was so paranoid about doing safe isolation (failure to do this was instant ejection from exam for safety reasons) that l flicked off the main switch, then the isolater, then locked off, then the MCBs. Yeah l know the totally wrong order.

Does the same apply to then RCDs Teletrix? Should they be opened as well before opening Main Switch?
 
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pushrod

  • Thread Starter Thread Starter
  • #7
still struggling to understand the difference here, can anybody give me some more examples of the two different types please?

As you correctly said switches are designed to be operated under load whereas isolators are not. They are basically doing the same thing but there are subtle differences. Switches will usually give you functional control of something and because they are designed to be operated under load the separating contacts are often specially hardened to resist the effects of arcing and they are also separated more quickly to reduce the chance of arcing.

Isolators will more likely be used to remove the supply to a circuit/s possibly for maintenance/repair. Because they are supposed to be operated without a load the contacts are not necessarily hardened and are not separated so quickly. If they are used as a switch it is common to see arcing (flashes) and for the contacts to be damaged.
 

ExArmy

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Arms
thanks, that explains it.
it wasn't me who asked the original question btw, it's a 2 year old thread.
 

telectrix

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Mentor
Arms
Esteemed
So l am doing something right then. I regularly turn off MCBs before turning off the main switch. It's a practice ive followed because of something my tutor told me regarding sparks appearing at the main switch, if you don't.

However due to nerves on my Level 3, l was so paranoid about doing safe isolation (failure to do this was instant ejection from exam for safety reasons) that l flicked off the main switch, then the isolater, then locked off, then the MCBs. Yeah l know the totally wrong order.

Does the same apply to then RCDs Teletrix? Should they be opened as well before opening Main Switch?
if the MCBs fed by the RCD are opened, then there is no load on the RCD and therefore none on the main switch, so answer is it don't matter.
 
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pushrod

  • Thread Starter Thread Starter
  • #10
thanks, that explains it.
it wasn't me who asked the original question btw, it's a 2 year old thread.
Doh! Caught again :D
 
K

Knobhead

  • Thread Starter Thread Starter
  • #12
Well I’ve written it now so I’m posting it!

An off load switch has no facility to break the arc caused by the load.

On load has various methods of breaking the arc:
  • High speed opening with sufficient air gap
  • Arc splitters
  • Blow out coils
  • Arc chutes

On load can then be divided in to several types
  • Load making / load breaking
  • Fault making / load breaking
  • Fault making / fault breaking

Sorry to add to the confusion but you must do some study in the subject
 
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