the insanity of grounding DC side (was Re: DC-GFP/2 protection [RE-wrench

[Hugh Piggott]

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At 5:34 pm -0700 25/8/02, Lawrence  Elliott wrote:
>..<loads of very humourous stuff>..
>I'm sure we are all familiar with the funny story about the "sycophants"
>who sourounded the king and insisted that the king was fully clothed
>when in fact he was "buck naked with his winky hanging out "   (Since
>Hugh is a Scottsman and a fine one at that I feel conpelled to use a
>slang he feels familiar with)

Just because I live in Scotland does not mean I have tartan growing 
out of my ears.  I think you are making a big emotional issue out of 
the differences between two equally safe approaches to electrical 
wiring.  Here in the UK we ground ('earth' actually) the neutral like 
you do in the USA.  It makes sense in many ways.  I can see that the 
other way has its advantages too, but I do not see any kings 
wandering around with or without kilts.  In either case you will need 
to have ground/earth wires throughout the system for safety.

>do not take it as an offense
>but rather an invitation to "enlightenment"

I look forward to learning something here (but not with much 
expectation, to be honest).

>
>If the majority of Europe feels it is unnecessary to ground a conductor
>( yes Todd I also feel it is an invitation to electric shock that
>originally did not exist) then we must assume two things.
>One is that all the engineers in Europe are sadistic since they like to
>see fellow citizens "fried" by all that nasty current .
>Secondly they must be technically incompetent.

It's a different system which has grown up with different 
conventions.  It works within its own context.  Its rules may not be 
so easily applied in a country where grounding of neutral conductors 
has been the norm for many decades. I do not believe it is safer or 
less safe or incompetent or any such thing.

>If I pee each day on my ground rod and dump salt each hour I  still have
>at least several kilo ohms to ground.
>Get real please

The resistance of the grounding electrode is an interesting question 
for debate, but not central to the issue of bonding neutral 
conductors to the grounding system.  I personally think the actual 
'ground rod' is one of the least important elements in grounding. 
What matters to me is the equipment grounds, bonding of extraneous 
objects such as water pipes, and whether this equipotential system is 
bonded to any live wires in the system.  Equipotential bonding of all 
exposed metal work (and connection to 'ground itself' where feasible) 
is a good start for electrical safety.  I worry about tower grounding 
which is not bonded to the rest of the system, because it relies on 
the ground rods to carry away any fault current which could otherwise 
raise the whole tower to lethal voltages.

>
>
>  Here is a question for all those who still feel the king has no reason
>for embarassment.
>
>If the current in any series circuit is equal in all parts of the
>circuit why would the NEC require two overcurrent devices in a circuit
>that is ungrounded and less than 50 vdc.

The overcurrent devices are there in case of a fault.  You only need 
one overcurrent device when you ground one conductor.  You only have 
one live conductor left to worry about.  If the system is floating 
then both conductors are potentially live, and need protection.

>Answer is " all principles of physics and common sense must and shall
>from this day forth follow only the principles of economics as put forth
>by Adam Smith"
>Of course he was an Englishman!
>Must we say more?

Many of you yanks seem to be much too obsessed with nationality and 
race and stuff like that.  I do find it offensive at times, and 
certainly irrelevant.

This has been an interesting discussion at times previously.

At 8:03 am -0700 23/8/02, Bob-O Schultze, Electron Connection wrote:
>I do not ground the DC side on 12 or 24V systems. I always plonk in 
>a ground rod for lightning at the array (five at a wind tower) which 
>I DO NOT tie into the electrical grounding system. I also use 
>lightning arrestors on anything coming into the house or power shed. 
>I've had nearby strikes turn inverters off a few times, but so far, 
>never a fry and die.

At 2:29 pm -0400 24/8/02, Rob Wills wrote:
>Every August 5-10 inverters came in with
>lightning damage.  When asked "is the dc grounded" the customer invariably
>said "no".  And it's not the grounding that saves the inverter - it's
>bonding inverter case to DC negative.

It seems as if the jury is still out on whether to ground the battery negative.
-- 
Hugh

http://www.scoraigwind.co.uk/

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