Recent Posts

Pages: [1] 2 3 ... 10
1
There will always be some earth current, unless you're floating in mid air, it might be micro amps but there will be some path to earth if the system is earth referenced.

The example you give is not really relevant to the safety of a standard electrical installation whatsoever in any case. You have created an insulated matting and adapted your behaviour to avoid creating earth paths by your own admission - hardly typical of the usage of standard electrical appliances.

Regardless, this is a moot discussion, I clearly stated in my post that protection would only be provided if the fault current exceeded 30mA.
We're in agreement so I don't see what we're adding to the discussion at this point.

Or are you in fact arguing in agreement with the OP that we should do away with earth referencing and RCD protection and go with unmonitored floating installations?
2
Hang on, scratch that Ross, I fully qualified in my original post that the fault current would have to exceed 30mA - directly under the line you quoted.

And I contend that there are plenty of times when standing, working on something where there would NOT be any earth current if you got tangled up across active/neutral and that therefore the RCD would NOT operate.

My workshop floor for example, has large rubber mats - mainly to reduce foot and leg fatigue.
Over my many years working on stuff, I tend NOT to lean against or otherwise contact the metalwork of equipment, switchboard frames, equipment enclosures etc.
So tell me where the earth current would come from when I've got the covers off a "thing" and get myself across Active and Neutral??
3
Hang on, scratch that Ross, I fully qualified in my original post that the fault current would have to exceed 30mA - directly under the line you quoted.
4
I agree wholeheartedly Ross, the fault current to earth would still have to exceed 30mA of course, I was merely trying to illustrate that the standard approach at least has a chance of working in that fault scenario. Some current will certainly flow to earth however so I don't think "may" is appropriate, the only uncertainty is around the quantity.
An unmonitored distributed isolated system has a far greater chance of causing unintended death however.
This thread is rife with practices that should never be followed.
5
Very interesting concept. Ive not seen it before. At first I misunderstood the term "unfolder"  This circuit is then only used for the timing synchronizer? Seems like it should work for that but the proof be in the actual performance. Be best to build it on breadboard and watch how it behaves with scope. 

If this is your complete circuit and not just a timing reference then i would say not a good idea. It only switches once per half cycle which would produce much distortion (any energy that falls outside or inside of the sine curve). Most grid tie inverters switch many times per half cycle dumping their power into an electrical flywheel (inductor) which outputs a true sine curve matching the original plus some current flow. Impossible to do this with only one switch per half cycle unless you used a class c amp with inductor and capacitor tank circuit tuned to 50/60hz, be tough to deliver any appreciable power though. From what Ive read H bridge is only way to go above a few hundred watts.  Anyway, have fun with it!

6

The only way of getting a shock is by touching both the live and neutral at the same time.. which an RCD won't protect against anyway.
This is incorrect, in a normal neutral-earth bonded installation with RCD protection where someone touches live and neutral at the same time, current will flow to earth as well as from live to netural through the person's body.

I hate to correct your "correction", but you are also in error under certain circumstances.

If you'd said that current "MAY flow to earth" and indicated that the RCD "MAY" trip, I'd have left it.
There are plenty of cases where there is insufficient out-of-balance current to trip an RCD, and I can testify to it myself.

Electrical Safety equipment certainly increases your chance of survival significantly, but it doesn't guarantee to save you in 100% of instances!
7
2) i know that industry practice is not to bond the batteries like this due to the fear of dead cell's, but each battery has a hydrometer and the status of the battery bank is monitored so cell death would be easily spotted. what this method does give as a bonus once that fear has been eliminated is the equalisation of all charge and discharge paths from one end of the bank to the other, improving the battery banks charecteristics.
It is possible that at some point you will develop a short in one of your cells - which could happen at any time, will just take a piece of plate material to drop off in an unfortunate position.
When this happens, that cell and all the other cells which are in parallel with it will discharge through it at high current.
If you're lucky, this will only mean that you destroy every block in that parallel string but it is far more likely that you will have a significant thermal event - fire and / or explosion when it happens.
If not, you will just kill all the other blocks in the pack from overcharge as your generator will likely kick in immediately and overcharge the surviving blocks.
It's possible that this may not happen within the lifetime of your installation, but you're certainly rolling the dice.
8
Haven't been here in a while, just to recap on your earlier post.


The only way of getting a shock is by touching both the live and neutral at the same time.. which an RCD won't protect against anyway.
This is incorrect, in a normal neutral-earth bonded installation with RCD protection where someone touches live and neutral at the same time, current will flow to earth as well as from live to netural through the person's body.
To quote yourself, current takes every path available, not just the one of least resistance. This at least gives a chance that the RCD will protect the user assuming the fault current to earth exceeds 30mA - which is quite likely.

in a neutral earth bonded system you could touch the live and earth at the same time to get the same result so in this respect it's actually worse.
While I understand that you are saying that there is an increased number of fault scenarios, my earlier point stands and a servicable RCD will definitely trip in a live to earth fault.

Also if we removed the earth altogether from the system and isolated the inverter so it wasn't earthed either and throwing away the rcd, that would ironically be the safest option. Birds don't get electrocuted sitting on the live wire as in this situation we have an isolation transformer we shouldnt get a shock either.

The only way something could go wrong is if another appliance shorted "neutral" to the same physical ground or casing you are in contact with and also touching the live wire.
You have correctly identified the flaw in this scheme. Without monitoring, the supposedly isolated system can become referenced to earth at any time and you will be unaware until there is a fault.
Just remember that the live could just as easily be referenced to earth as the neutral. Initially this won't cause an identifiable problem. However this could lead to the casing of your inverter (or any other connected appliance) assuming a potential of -230V if there was a neutral to case fault on any appliance (which is of course isolated) potentially delivering a fatal shock to anyone that comes in contact with it.

As far as i can tell the only reason the RCBO wont trip is because youre not getting a shock.
You are correct but you now have no way of testing your RCBO in your installation so you have no idea if it will work when you need it or not.

I have a gut feeling the entire electrics industry grounds neutral for voltage stability and pretends in some far fetched situation it provides safety.
I'm sure you're joking and can appreciate that international electrical specifications are drafted by well meaning educated professionals - pro bono in my country, in the interest of public safety.
9
Maximum Power Point Tracking
10
Utilities / Re: Electric Fence Zapper
« Last post by winger on April 24, 2017, 01:49:07 PM »
Hello,

I finished my 220 volt version energizer. For testing I only have fence voltage tester with, I think, neon lamps. The higher lamp is rated as 6000 volts. So if I test fence near to it connection to energizer, then all tester neon lamps is burning bright, so there is at least 6000 volts, but after approximately 500 meters, neon lamps burns only till 4000 volts ratting. I thinks problem is with fence earthening. For now I have three one meter long spikes which is placed three meters apart from each other. Maybe someone can tell how to make correct earhtening for this kind of fence. Thanks.
   
Pages: [1] 2 3 ... 10