earth leakage rating for 63 amp 400V socket outlet 3

[simisteven]

We have numerous 63 amp socket outlets, 400 3 phase VAC (50Hz) for powering fans etc in our plant. Traditionally they are protected by overcurrent MCBs which have integral earth leakage protection (RCD) rated at 30 milliamp.
Our national wiring regulations stipulate EL protection for 16 amp 230 volt socket outlets however there is no stipulation for 400 volt systems.
I wish to replace these 400V EL units from 30mA to a higher rating because we experience a lot of spurious tripping.
Any thoughts on this?

 

[waross]

Our code stipulates a minimum insulation resistance for systems and branch circuits. At the code minimum resistance there is no thought of nuisance tripping due to resistive leakage current.
If the branch circuits are tripping at 30 mA that's about 20 Watts of loss. That seems a little high.
The nuisance tripping may be signalling you that the fan motors are approaching the end of their insulation life.
I would first check the leakage current on the circuits with the fans connected and with the fans disconnected.
If this is a new installation, with very long branch circuits, you may have capacitive charging issues. If the current is capacitive and spurious tipping has been an issue since new, your options may be to change the branch circuit conductors for conductors insulated with a material with a lower capacitive constant, reduce the length of the branch circuits with the installation of sub panels closer to the loads or the installation of small reactors on each circuit to divert the capacitive current from the trip units.
I would only increase the trip settings as a last resort and after an investigation of the cause of the tripping.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

I suspect that you have added more and more VFDs to your installation over time. They draw lots of capacitive leakage current because of the steep edges in the motor voltage wave-form. One way around this is to reduce the switching (carrier) frequency as low as possible. That usually helps.
If that doesn't help, an isolation transformer may be needed.
There are motor inverters with sine-wave output. They have very low capacitive leakage and have been used with cable lengths like 300 meters without problem.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[LiteYear]

Here in Australia, 30mA RCDs are only required for <=20A general purpose outlets. No requirement is given for >20A or dedicated purpose outlets. In our laboratories we have 30mA RCD protection on all the 10A and 15A single phase outlets, but I believe the higher rated 3 phase outlets have "machine graded" and opposed to "personal" RCD protection. I think the trip level is more like 60mA. We understand it to be insufficient to save your life but probably good enough to prevent a fire.

The motivation in that case is because all sorts of funny things in various states of development are plugged into those outlets, and only by authorised, competent people, a higher trip level makes a significant dent on nuisance tripping.

 

[simisteven]

Hi Liteyear. The only publication I DID find on the internet was an Oz one and it mentioned RCD for 63 amp outlets. However, those outlets were 3P+N+E and it was very clear that neutral must be connected for the RCD to work properly.
My sockets are 63 amp 3P+E as they supply motors only.
Generally MCCs feeding motors do not have earth leakage protection, although they do have earth fault protection in larger motors.
I am busy trying to get a recommendation from M&G on what ELUs (RCDS) to use.
MY original question also relates to the fact that we are using 3P+N RCDs and NOT supplying a neutral, so will this cause problems.
In answer to Waross, these fans are fairly new.
In answer to Skogsgurra, these outlets are not supplying VSDS just 3kW 400V 3 phase DOL motors.
There ARE four large VSDS inside the same substation though.

Thanks for your thoughts gents.

 

[ScottyUK]

RCDs will work fine on a grounded 3-wire system. The problem you will probably have is that the test button won't work: the test button bleeds a small amount of current around the sensing toroid to simulate a low-level fault, and the resistor is almost always connect line-neutral.

 

[LiteYear]

I double checked and our electrical lab protection is "equipment" grade and is actually at 300mA.

The authoritative sources in Oz are the workplace health and safety laws, made accessible by Safe Work Australia, and the standard "AS/NZS 3000 Wiring Rules" which is mandatory under those laws.

Not having a neutral is not a problem for RCD operation. The RCD's test circuit however, does need to be suitable (no big deal, just a couple of ways to do it).

 

[simisteven]

thanks Scotty and Liteyear, that makes a lot of sense to me.

 

[Kiribanda]

simisteven,
It looks like you are from the "IEC world" where your installation code is IET Wiring Regulations for Buildings 17 th edition (BS7671) or a local code based on IEC60364 and your LV earthing method is TT.Per IET Wiring Regulations,all 230 V socket outlets have to be provided with 30mA or less RCCDs for human protection. Because these 230V outlets are mainly used in houses,offices by unskilled ordinary people.Now 400 V outlets are mainly for indutrial use where welding plants,portable pumps etc are connected and use.Per IET Wiring regulations the earth leakage protection for these 400V circuits can be provided by overcurrent devices for TT earthing method.One should expect small leakage currents from the equipments connected to these 400V outlets, and therefore if you install RCCD devices for earth leakage protection, then it will give nuisance tripping.Therefore,in my opinion, (1) provide earth leakage protection by 30mA RCCDs for 230V outlets (10mA for swimming pools)as you have already done (2)No need to provide earth leakge protection using 30mA RCCDs for 400V outlets.But make sure that the overcurrent devices connected to these 400V circuits DO provide adeqaute earth leakge protection by measuring/ testing the earth loop impedance (Zs).Hope this helps.

 

[ScottyUK]

Why do you assume a TT installation? They are relatively uncommon in the UK these days; most industrial systems are TNC-S or TN-S. Earth leakage protection to protect against fire, or where earthing conditions are indifferent, or where it is difficult to achieve the required disconnection time is perfectly reasonable - remember that BS 7671 is a minimum requirement, not a design guide, and complying it is NOT a legal requirement. Complying with BS 7671 is by far the simplest way to discharge your duties under the Electricity at Work Regulations, the ESQC Regulations in some cases, and the broad-ranging HASAWA 1974 - all of which are legal requirements - but if you achieve equivalent safety while not strictly complying with BS 7671 then that is a legally acceptable option. Of course you might have to defend such a course of action under hostile cross-examination in court, so on balance it is better to comply with BS 7671 in my opinion.

 

[Kiribanda]

ScottyUK,
Why do you assume a TT installation?
I just assumed it to be TT because most of the eastern countries are having TT.
Anyhow even if the earthing system is TNCS or TNS then both 400V & 230V outlets can be easily provided with earth leakage protection using OCPDs subjected to the condition that it satifies the loop impednace given in 17 th edition.

 

[ScottyUK]

I'm just curious - whereabouts are you located? You often reference British codes and have a good understanding of our wiring regs, but I have a feeling you might not be in the UK from that post.

 

[simisteven]

Hi Scotty and Kirbanda.
Kirbanda spot on with your observations. I deliberately do not refer to socket outlets because we are NOT supplying them via this 4 pin 63 amp sockets. We mostly certainly do have extremely strict wiring regs and all 230v 16 amp socket outlet must have 30mA EL protection, not negotiable. I can remember doing 16th Edition in the UK back in 1998, I think it is 17th or even 18th now. In those days socket outlets did not require RCD by law but it has probably changed now.
Scotty I am in South Africa. I spent 9 years in the UK so I got pretty familiar with the various regs you have there. Many if not most electrical and safety regulations in South Africa have been adopted over the years from British and European standards especially in mining industry where I used to work.
many thanks for assistance chaps.

 

[ScottyUK]

We're on the 17th Edition now. A major change, for the domestic and commercial guys at least, is that all hidden cables which aren't protected by earthed metal containment or armour must be protected by 30mA RCDs. In a home or office environment that is pretty much everything; sales of RCBOs have rocketed.