Use of "Emergency Stop" CB2 on MEP-002a/MEP-003a ?

[Chainbreaker]

Just curious if anyone knows the advantage of using the Control Panel's "Emergency Stop" (CB2 DC Circuit Breaker) vs flipping the AC circuit breaker off and using Master Switch to turn off unit in an emergency stop situation other than saving a second or two?

Does using the Emergency Stop just de-energize the stop solenoid and the generator is stopped while producing AC power if in use? Or, does using the Emergency Stop somehow trip the AC Circuit breaker and kill the stop solenoid at the same time for a proper shutdown sequence?

 

[dmetalmiki]

I do not know the definitive answer, no doubt a 'sparky' will chip in. But like most things that run, and generate power, or power equipment, It might be very necessary to " shut off and run" OR Isolate 'something OR SOMEONE' pronto in one swift (and easy) movement.

 

[DieselAddict]

The main difference between using E-Stop and the "off" switch is that the E-Stop kills all the control power in the panel. Both kill the AC output.

 

[Guyfang]

We were told to always deenergize the S-5 AC interrupter switch before turning off the gen set. The CECOM wiesel claimed that the K-1 relay tended to not have as many problems with the contacts, when S-5 was used. The contacts opened immediately, and there was less arc at the contacts. That's the party line. I am not sure it's true, but I always did it that way.

 

[Triple Jim]

Maybe I'm being dense, but the schematic shows S5 as being the oil pressure switch. I'm thinking you mean CB1, but...?

 

[Guyfang]

My mistake, I looked at a schematic for the 803!

 

[Triple Jim]

So the advice is always turn off the main breaker before shutting off the generator? That is part of our usual procedure here. I wrote up a step by step procedure, and other family members have shown they can safely get the house on generator power if the commercial power goes out. Once I even arrived back in the driveway, got out of the car, and heard the generator running. Pretty surprising the first time a wife does it by herself.

 

[Guyfang]

Yep, always turn off the CB-2 first. Its kinda like shutting the main breaker off, on your house, with everything in the house still running. You get a much bigger arc. And closing a main breaker with the load still turned on is even worse. That's why we wear special clothing and a face mask when turning on, or off, the big transformers. WHAT A BEAUTIFUL SIGHT!! The arc is incredible. And, for me, scary,

 

[DieselAddict]

For me personally I disconnect as much load as practical and verify on the load meter that its under 25% before I open the load breaker on the generator. This greatly reduces arcing on the contacts. More of an issue if you are running inductive loads.

When I'm testing generators I'll drop and disconnect full rated load BUT that is all resistive and the arcing will be minor. As a normal operations I like to see the load 25% or less when making those transitions.

 

[snowtrac nome]

reading the tm, you are supposed to disconnect the load and let your windings cool before shut down. that should answer the why you don't shut it off with the emergency breaker unless it is a real emergency.

 

[Chief_919]

The only real uses the emergency shutdown were intended for were:

Someone is getting electrocuted and you need to stop power ASAP.
Some sort of tactical event demands you shut it down ASAP.
The rest of the controls don't respond and that is the only way to shut it down.

 

[Triple Jim]

Here's what an arc looks like: https://www.youtube.com/watch?v=hIkNY5xjy5k

 

[glcaines]

When I shut down my MEP003a, I first disconnect the entire load via my 400-amp manual transfer switch. I don't reduce the load in the house prior to shutdown. I then let the genset run with no load for 10 - 15 minutes to let it cool down and then shut it down via the switch. I never reduce the RPM prior to shut down. I've been doing it this way for years and have never had any issues with the genset.

 

[Chainbreaker]

Thanks for all the replies. The reason I had the question was to verify whether the "Emergency Stop" DC breaker had any effect on the main AC output circuit breaker or not. Your replies answered that question, that it DOES NOT have any ability to initially trip (CB1) AC circuit breaker when Emergency Stop is used. So, the only reason I could see to use the "Emergency Stop" (CB2) DC panel breaker would be during an actual PANIC SITUATION that occurred requiring IMMEDIATE ACTION where time was of the essence - unit on fire, smoking electrical short, or other imminent danger.

Other than dealing with a true emergency situation, it sounds like it would still be best to turn off the AC circuit breaker first (when possible) and then use the Emergency Stop lets say...if (S1) Master Switch were somehow to become inoperable/non-responsive while unit is still running (non-emergency).

Otherwise, its ALWAYS standard shutdown procedure - remove load or as much as possible, then AC breaker off, then Master Switch to off.

 

[Chainbreaker]

Yep, always turn off the CB-2 first. Its kinda like shutting the main breaker off, on your house, with everything in the house still running...

I think you meant CB-1 the unit's AC Circuit breaker. CB-2 is the control panel DC Emergency Stop circuit breaker. I know, I know...probably too many generators/schematics floating around in your head?

 

[snowtrac nome]

this is a good point unlike standard diesel engines ,you should turn your generators on and off at 60 hz otherwise your voltage regulator wont be long for this world.