New DEC museum entry :D

[Bob Bradlee]

On Tue, 20 Feb 2007 22:47:05 +0000, Adrian Graham wrote:

>On 20/2/07 21:48, "Tony Duell" <ard at p850ug1.demon.co.uk> wrote:

>> THat's an odd fault. It's repeatable, yes? In other words you turn it on,
>> it runs for 5 minutes, then trips the mains. You cna then power it down,
>> power it up again and it'll run for another 5 minutes...

>Yep. Every time. I haven't timed it exactly, but it will run for minutes
>then give up; last night I had enough time to start playing with DCL and
>leave it for a bit while I dug a manual out. Then everything went black :)
> 

I had a problem like that, where I had a rack that was drawing close to the limit on a 20 amp breaker, 
when I added the last system to the stack the problem began, after a few minutes of runtime the breaker 
would heat up and pop, I swaped the breaker out with a different one of the same size and it that held just 
fine. The circuit I moved the week breaker to, normally only runs 7 or 8 amps and it never failed with the 
light load.

I had a second breaker problem. After an extended power failure, I found that the circuit would not carry 
both the normal startup load with the additional of 2 large UPS's at full charge rate on near dead batteries 
during startup. Just about the time everything booted and came back up, the breaker would have heated 
up and poped. I pulled the external battery packs off, and let them charge the internal batteries first and 
then added one external pack at a time, untill I could get a larger circuit run to the rack.

While you are at it, you might want to take a clamp on amp meter and balance the load between phases. 
You may be pulling more power on one phase. If you pull the voltage down on one side or phase with an 
unballanced load, the current load will go up and breakers will be more likely to overheat and pop.

I was in a 3 phase box just yesterday that was running 17a, 23a, and 37a on each of the 3 phases.
The electric company bills based on the max load on any single phase, by moving about 10a of load from 
phase 3 to phase 1, we dropped the billable load the electric company sees from 37a to 27a, close to a 
third. That should look good on next months electric bill. 

Just a thought, back under my rock .... 
The other Bob