Relt switch

T

The electron man

Senior Member
Location
Nyc
Occupation
Electrician
So I am installing a switchgear and I see a small dial on the gear labeled main relt switch I asked my foreman what it was and he had no idea what's the main relt switch for
 
Could be shorthand for Reduced Energy Let Through... basically an override to your usual breaker trip settings in order to knock down the arc flash energy during maintenance.
 
The electron man said:
I'm guessing this reduces the arc flash on the load side of the main switch gear not the line side ??
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I know nothing about them; I'm just good at finding stuff.

I would guess they reduce fault current everywhere, so they would reduce series arcing everywhere, but parallel arcing only downstream.

Then again, I'm guessing that parallel arcing is what really matters.
 
LarryFine said:
I would guess they reduce fault current everywhere, so they would reduce series arcing everywhere, but parallel arcing only downstream.
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Arc Flash has nothing to do with series or parallel arcs. Those term are associated with Arc-Fault.

Arc Flash is what sends 'electricians' to the hospital, it is why PPE is needed.
 
jim dungar said:
Arc Flash has nothing to do with series or parallel arcs. Those term are associated with Arc-Fault.

Arc Flash is what sends 'electricians' to the hospital, it is why PPE is needed.
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If there is a phses to phase short on the load side of the main i see how the relt will reduce the arc but how would it help on the line side ?
 
The electron man said:
If there is a phses to phase short on the load side of the main i see how the relt will reduce the arc but how would it help on the line side ?
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The RELT causes the circuit breaker to react to the fault faster with the hope that it clears the arc sooner.
Protective devices can only protect downstream equipment, they cannot protect themselves or upstream. The downstream equipment needs to be 'physically' remote from its protecting device by barriers.
 
It is used whenever you work on the gear, as others have said, reduces the arc flash potential energy. If left in that position though, could cause nuisance trips.
 
I think this is especially important in the larger time delay breakers used to allow for a longer duration of over current because of things such as high motor starting loads and not trip, but when working/trouble shooting on live equipment or lines you want to limit the time the overcurrent or higher current would be allowed through in event that current is arcing in your presence. (Arc flash) By limiting the duration of the arc event, it reduces the potential impact to persons working on it.
I think someone would get mad at you if you forget to reset the time delay and the equipment or motor keeps tripping the breaker.
 
hillbilly1 said:
It is used whenever you work on the gear,
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A RELT is used when working on downstream, physically separated gear.
It does nothing for the gear in which it is installed. Thus is a common misunderstanding with main devices in multisection switchboards.

My suggestion was always for Main devices to be in standalone sections with cable and conduit feeds to distribution sections. But people don't like the cost and the extra real estate.

Has any manufacturer developed a switchboard barrier that they advertise as stopping arcs?
 
jim dungar said:
A RELT is used when working on downstream, physically separated gear.
It does nothing for the gear in which it is installed. Thus is a common misunderstanding with main devices in multisection switchboards.

My suggestion was always for Main devices to be in standalone sections with cable and conduit feeds to distribution sections. But people don't like the cost and the extra real estate.

Has any manufacturer developed a switchboard barrier that they advertise as stopping arcs?
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It does nothing for the line side, but it is for anything on the load side.
 
hillbilly1 said:
It does nothing for the line side, but it is for anything on the load side.
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Not for direct connected equipment.
Say you have a multisection switchboard with the RELT on the incoming main switch. Now say you have an arcing fault on the line side of a breaker in section #2. The arc will move move away from its point of origin and travel along the bussing towards the main device. How do you know the main will clear the fault before it is engulfed and bypassed by the arc?
 
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