[Elecraft] To Fuse or Not To Fuse...

[G3VVT@aol.com]

The safe answer is to fuse the +ve leg of the DC power cord.

The K2 is protected internally by F1, but everything upstream of this is not. 
This includes the power connectors, C196, D10 and anything connected to P3, 
Aux 12V. I use a fuse with at least a 50% uprating of the maximum current drawn 
by the device to allow for surges at switch on. In the case of the K2's max 
of 2.5A will be about 4A or so in available values using a plain fuse. This 
could be derated using an anti-surge fuse to closer to the maximum device 
current. Experimentation is called forin final selection of the fuse size. All of my 
power cords for any of the station and mobile equipment are fused in this 
manner.

What could disaster could happen in the case of a short and with Murphy's 
assistance: a fire is the answer!
All depends on the battery's ability to supply the necessary current and the 
ignition point of the power cable and anything inflammable next to it.


The item of isolating the grounding of a work surface with a 1M ohm resistor 
is well put.

Only this week I had the misfortune to be present across the AC power on a B&
K counter I had on the repair bench. Apart from an extremely sudden rush of 
adrenalin there was no apparent damage to my person. Had the workbench been 
directly grounded, it could have put my "lights" out for good as I got across the 
live side of the AC supply.

We were forced by UK government legislation in the late 1970's to install 
RCCB's (residual current circuit breakers) in all TV repair shops. On 
experimentation done at the time it appears it would be unwise to allow more than 10 to 
20mA of AC current to flow though your chest. At 30ma of current you are 
extremely aware of the problem and it could effectively stop your heart by sending 
it into fibrilation? As a continuation to this legislation the practice of 
fitting RCCD's in the domestic environment in the UK at least is apparently now 
mandatory on all new houses and power installation. Not sure what the term for 
these in the USA, but have seen them listed here as ELCB, RCD or RCCD. Possibly 
Ground Leakage Circuit Breakers?

It's the volts that jolt, but it's the mills that kills.

Regards,
Bob. G3VVT


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