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achjimmy
22nd Dec 2018, 10:40 AM
Slowly setting up the workshop . Most of the machines will be wired through a vass busbar. I couple of the machines like the 3phase bandsaw are quite old. The mill, lathe and drill don’t have a neutral . The sparky who I’ll get to set up the sub mains has suggested We use a 4 pole RCD over everything then individual breakers (there is hrc fuses on each busbar take off.

I like the Saftey of an RCD on all its just am a little dubious with some of the old welders and machines that they’ll trip the earth leakage !

Michael G
22nd Dec 2018, 11:30 AM
Earth leakage devices look at the current in and the current out, and if there is more than a pre-defined difference, trip. I'm not sure that they will be the problem. I think the bigger issue will be the breakers that you install, as there are various types, depending on the device that they are connected to. I know there is a type that is better for using on circuits with welders on for example.

Michael

eskimo
27th Dec 2018, 11:11 AM
yep...rcd's and older equipment could be a pain..but usually only where old electronics are concerned, where they wire in caps etc to earth to do filtering...
but until you start having problems you wont know...they can always be taken off the RCD circuit later...just make sure the rcd is fitted at the sub-board in the shed...and not the main board.

Theberylbloke
28th Dec 2018, 08:23 PM
Hi achjimmy,

AS3000 has very recently changed and now stipulates all sub-circuits to be protected by RCDs in residential situations. I'm not sure if each sub-circuit has to have it's own RCD or whether one RCD/MCB combination can be used as a main switch and thus cover the sub-circuits.

Given that RCDs are a primary protection from active to earth shocks (also fires!) I'd be more inclined to find out why a particular machine causes nuisance RCD trips and see if it can be fixed.

Cheers

The Beryl Bloke

.RC.
28th Dec 2018, 09:56 PM
Earth leakage devices look at the current in and the current out, and if there is more than a pre-defined difference, trip. I'm not sure that they will be the problem. I think the bigger issue will be the breakers that you install, as there are various types, depending on the device that they are connected to. I know there is a type that is better for using on circuits with welders on for example.

Michael


That can't be right. The electricity gets consumed remember. A kettle says is "uses" 1000W.

So less must come back then goes in. :)

What I wrote above is probably a common misconception.



If I have learned correctly then it is more the wattage is the amount of force needed to push electrons in a circuit.

russ57
29th Dec 2018, 04:34 PM
The electron flow 'in' and 'out' must be the same. If less 'comes back' (via neutral by convention) than goes out, some is 'leaking' to earth, hence the 'earth leakage' device, or 'residual current detector' trips.

But capacitive coupling, either parasitic or via noise filters mean that a small amount of leakage is unavoidable so the limit is typically 30mA.

But as far as I know, there are others available designed for particular purposes which have different limits, and also different time sensitivity.

The power used is measured by the voltage drop across the device (240v) times the current.

Russ

simonl
4th Jan 2019, 09:55 PM
Hi there,

I have 2 machines that are over 60 years old, still with original 3 phase motors. These have never triped the RCD. Realistically, if there is any current leakage to earth then it's best to find out because an RCD has tripped rather than from you or someone else receiving a lethal electrical shock.

Simon

BobL
6th Jan 2019, 12:00 PM
The electron flow 'in' and 'out' must be the same. If less 'comes back' (via neutral by convention) than goes out, some is 'leaking' to earth, hence the 'earth leakage' device, or 'residual current detector' trips.

Just to add to the confusion there's no actual electron movement in one direction in AC circuits. The electrons in the wires move back and forth less than a mm during the 1/50s that a standard AC cycle takes to complete. Despite this, AC currents (in AC its the back and forth movement of electrons) can be easily measured by measuring the small V drops across a very low value resistors in the circuit

jhovel
6th Jan 2019, 12:48 PM
That can't be right. The electricity gets consumed remember. A kettle says is "uses" 1000W.

So less must come back then goes in. :)

An easy way to think about it is the analogy to water: imagine a waterwheel or turbine. THe amount of water going over/under or through it doesn't change. THe energy extracted is from the potential or force of the water, not the water itself. Same with electricity. The amount going in and out stays the same, no matter where it goes - back in Neutral or leaking to Earth.

paul33
7th Jan 2019, 11:16 AM
Hi there,

I have 2 machines that are over 60 years old, still with original 3 phase motors. These have never triped the RCD. Realistically, if there is any current leakage to earth then it's best to find out because an RCD has tripped rather than from you or someone else receiving a lethal electrical shock.

Simon

I have an old 3 phase milling machine, lathe and welder, none of these machines have ever tripped the RCD. Recently I had trouble with my air compressor tripping the RCD. This was a relatively new machine, single phase. The fault
was the motor run capacitor shorting to earth.

.RC.
7th Jan 2019, 01:26 PM
Speaking of RCD's I m not sure how widespread this story got around the country, but a week ago in north Queensland, a woman and her daughter were electrocuted to death through some odd occurance.

The media report was there was a battery charger connected to a truck battery and somehow they got electrocuted, the report also mentioned an electric fence was involved.

https://www.news.com.au/national/queensland/news/mother-and-daughter-electrocuted-on-queensland-property/news-story/e6ba75e95033495d00044bb84da813ba



Police said a family member had attached a cable from an electric fence to the bull bar of a semi-trailer to keep some horses from escaping.
It is believed the truck later became electrified when a battery charger was attached to the vehicle.

BobL
7th Jan 2019, 02:00 PM
Speaking of RCD's I m not sure how widespread this story got around the country, but a week ago in north Queensland, a woman and her daughter were electrocuted to death through some odd occurance.

The media report was there was a battery charger connected to a truck battery and somehow they got electrocuted, the report also mentioned an electric fence was involved.


Unless the pulses from the electrical fence fried something inside the charger the electric fence connection could be a red herring. Most probably something inside the charger shorted allowing mains V onto the truck frame.

paul33
7th Jan 2019, 02:07 PM
This news story was reported in South Australia. There was a photo of the wire connected from the fence to the bull bar. In the news story, it was not explained very well how the connection was made from the vehicle.

waxen
8th Jan 2019, 06:07 PM
[QUOTE=Theberylbloke;1944890]Hi achjimmy,

AS3000 has very recently changed and now stipulates all sub-circuits to be protected by RCDs in residential situations. I'm not sure if each sub-circuit has to have it's own RCD or whether one RCD/MCB combination can be used as a main switch and thus cover the sub-circuits.

Given that RCDs are a primary protection from active to earth shocks (also fires!) I'd be more inclined to find out why a particular machine causes nuisance RCD trips and see if it can be fixed.

Cheers

The "stipulation" as I understand it is that it's up to the Electricians disgression. I recently had my shed rewired with three non RCD protected circuits that are hardwired to machines fitted with VFD's. No more nuisance tripping.

BobL
10th Jan 2019, 09:09 AM
The "stipulation" as I understand it is that it's up to the Electricians disgression. I recently had my shed rewired with three non RCD protected circuits that are hardwired to machines fitted with VFD's. No more nuisance tripping.

I've had 8 VFDs for up to 8 years in my shed and the whole shed supply is on an RCD and have never had a nuisance RCD trip.

benhoskin
10th Jan 2019, 09:38 AM
The nuisance trip from RCD's can occur frequently. One solution is a time delayed RCD. These RCD's cost substantially more than your common RCD, but allow a small time when connected for the caps to charge in the RCD before they allow normal operation. They then behave exactly the same as a normal 30mA RCD.

waxen
10th Jan 2019, 09:51 AM
Not all vfd's trip rcd's. I have some Mitsubishi inverters that are fine, and some SEW's that are not.

Com_VC
10th Jan 2019, 02:19 PM
What is causing them to trip though? Could just be something as simple as a setting.

Vernonv
10th Jan 2019, 04:33 PM
I would have thought that ANY earth leakage from ANY piece of electrical equipment is an issue that should be resolved.

Grahame Collins
10th Jan 2019, 11:07 PM
The geckos in my shed get inside the gpo's and obviously short the switches. Until recently it was not a problem,
With a second freezer in there now, I have to check the RCDs every morning otherwise I may have a freezer full of bad meat.

The ants do a good good job of removing the zapped geckos but I do wonder can the switched gpo,s be sealed up without any detriment to them?

The odd thing is that it does not happen inside the house. We don't see geckos inside the house. Maybe they don't like the aircon.

Grahame

benhoskin
10th Jan 2019, 11:49 PM
The vfd's can cause the RCD's to trip through a couple of different means. Either by the charging of the internal capacitor bank or some vfd's contain filter circuit to minimise electrical noise on the circuit it is attached to. Neither of these occurrences can harm the operator, just creates an imbalance in the active/neutral lines and trips the rcd.

BobL
11th Jan 2019, 12:48 AM
The ants do a good good job of removing the zapped geckos but I do wonder can the switched gpo,s be sealed up without any detriment to them?


Yes they can be sealed.

Many years ago (pre RCD days) I was having breakfast when one of the 20A (non-RCD) house circuits tripped.
After some fruitless investigations inside the house I remembered that the same circuit also went down to the shed and when I threw open the shed door I was hit with the smell of acrid smoke and saw one of the GPOs under the window was smouldering and looking like it was about to catch fire.

What I worked out happened was ants had setup a nest inside the GPO.
This was pre-dust serious collection days and the GPO was also partially buried in sawdust which I guess made it nice and warm inside the GPO.
During a storm in the night, a small amount of rain had blown in under a window and entered the GPO such that the mix of water, fine sawdust and ant juice (formic acid) shorted the inside of the GPO.
So although the power was off the GPO and sawdust around it was still smouldering and developing into a proper fire - luckily some of the sawdust was also damp from the rain.
The inside of the GPO got hot enough to melt the insulation around the wires so they had touched each other causing the breaker to open.

That's when I decided to have RCDs adde to the house circuits, installed a sealed window in the shed and it became a driver to get some proper dust collection going.
An RCD would have switched the circuit off much earlier but just in case I also installed a fire alarm.

Vernonv
11th Jan 2019, 09:52 AM
The vfd's can cause the RCD's to trip through a couple of different means. Either by the charging of the internal capacitor bank or some vfd's contain filter circuit to minimise electrical noise on the circuit it is attached to. Neither of these occurrences can harm the operator, just creates an imbalance in the active/neutral lines and trips the rcd.I'm not saying that it doesn't happen, only that it shouldn't. I would suggest that that behavior is not "normal" and is caused by a faulty device (maybe only a "slightly faulty") or poor design.

benhoskin
12th Jan 2019, 05:25 PM
The fault is not a problem with the device.It is just caused by certain devices in normal operation.As long as that is what is causig the RCD to trip and not another wiring problem. Ideally it would not happen, and there is a solution, the time delayed RCD's, but not many people would like to pay for them. A three phase 32 amp rcd/breaker delay combo is ~$400 just for the part. It is actually not a bad thing if you do get the tripping. It makes you operate the RCD, this ensures that the trip mechanism is actually working and not stuck.

Stustoys
25th Jan 2019, 09:08 AM
The only issues I've had with old machines that would have been an issue for an RCD is two of them used earth as neutral.
Other than that the only issue I've had is if I turn off my compressor at the GPO the RCD trips, though if I let it turn itself off or use the switch on the compressor its fine. I assume the compressor has a double pole switch, but have never looked into it.


What brands of VSD cause nuisance tripping? I would like to be sure not to buy one.