RCD protection for portable equipment with Inverters

[clicon357]

clicon,
If you are suffering this much damage then the equipment being used is not suitable for the application, you have a "selection & erection" issue.
However I do understand the use of RCD's, but, IMHO this is a sticking plaster on a severed limb approach.

You would have to understand the nature of my industry. Traditionally the cradles were simple wooden frames hoisted up the side of buildings with hemp ropes. Now we have fully powered cranes with industrial plcs some of which the users have to interface with. Whilst the kit has changed the people using it haven't. Lets be honest if they were that technically adept they wouldn't spend their days wiping dirt off glass which it what it comes down to. Its not that well paid and clients won't pay for what they see as a menial job. Its sometimes an abusive environment with time pressures. Also at the top of the building it's a case of out of sight out of mind for some clients. Bottom line is that I ventured a solution to a similar problem experienced by the OP, it worked and continues to work. Can't add much more than that really.....................

 

[netblindpaul]

Clicon,
I am not criticising you solution per se, even though I am! Sorry!
IMHO I believe that I could prove that it does not meet CDM, EAWR89, & PUWER98.
IMHO your solution relies on what is now additional protection, rather than "fundamental" protection of the circuits.
Not quite the right terminology, but I am using it that way to try to illustrate a point.

 

[gerard]

This is just my experience - and I'm sure they are all not the same. I work in a factory - if someone gets a static shock there is a big fuss, they have to go home, fill in accident reports, take time off and with today's 'compo' culture, god knows what else. Hence the reason to have everything to standard

 

[netblindpaul]

gerard,
A "static" shock will be nothing to do with the fixed wiring installation.
In a factory environment, there are really very very limited requirements in BS7671 for RCD's.

 

[gerard]

gerard,
A "static" shock will be nothing to do with the fixed wiring installation.
In a factory environment, there are really very very limited requirements in BS7671 for RCD's.

I understand that - I am just making a point and I don't want to take any chances. If it is possible to put an RCD on the circuit - I will

 

[gerard]

Hi,
Just an update on the RCD/Inverter problem. I talked to the manufacturers of the Inverters and they said that the problem is not the leakage current, as I have already tried a 100mA RCBO, but instead the Inverters are too small for the motors ( alarm bells did start ringing - bet they though a quick sale here!). The motors in question stop/start due to the work they carry out, so they said when a motor is carrying out a task that requires it to stop/start all the time, the inverter should be the next size up. Apparently this will solve the problem of tripping RCD on Inverter circuit. Looking forward to your thoughts.......

Cheers,

 

[netblindpaul]

Quite possibly, what sort of load is it?
Is it luffing, rotating, etc. how much reflected inertia on the motor shaft?

 

[gerard]

They are two 1.5kW motors and they stop/start all day long - they feed pizzas into a stamper which stops the conveyor for the time it is stamping.

 

[netblindpaul]

OK so it's a conveyor that the inverter is driving?
Is it horizontal?
What is the make up of the conveyor?
What is the mechanical link between the motor shaft and the conveyor, direct, gearbox, belt drive?

 

[gerard]

OK so it's a conveyor that the inverter is driving?
Is it horizontal?
What is the make up of the conveyor?
What is the mechanical link between the motor shaft and the conveyor, direct, gearbox, belt drive?

Horizontal conveyor, about 3m long, 500mm wide, connected with gearbox to shaft. Conveyor stops/starts to allow product to be stamped/cut to size

 

[netblindpaul]

So basically indexing the conveyor.
Reduction gearbox I am guessing?
Motor is normal squirrel cage?
Large number of stop starts per hour, I would generally size the inverter one up from the normal duty for that motor in that application.
Though there are a few other factors I would consider.

 

[Kremnos]

Just use an inverter rated RCD

 

[gerard]

Yes. Yes and Yes. The manufacturer recommends up-sizing the inverter like you say - he said he has seen this problem before and this will solve the problem. Not exactly the cheapest solution though!!

 

[gerard]

Just use an inverter rated RCD

Kremnos - have you seen an Inverter rated RCD before?

 

[netblindpaul]

Yes. Yes and Yes. The manufacturer recommends up-sizing the inverter like you say - he said he has seen this problem before and this will solve the problem. Not exactly the cheapest solution though!!

Incorrectly sized in the first place then really.
I'm not convinced that it will stop the tripping problem though...
Be nice to see.