Uzzy
Hi-poster
Posts: 153
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Post by Uzzy on Jan 22, 2006 19:34:45 GMT
???Is there anyone with a good knowledge of inverters as I have just wired up my milling machine at last only to find that my main RCD pops. I have a small box in the workshop which has a 6a Type 2 ( Lights ) a 30a Type 2 ( Sockets ) and a main one with the following details LN 6316 Current Operated Circuit Breaker, 240V 16 A Double rated, 19mA Rated Tripping Current, 1500A Rated Breaking Current this is the one the pops. I have disconnected the motor from the inverter and it still pops, my concern is that the inverter its self is for the scrapheap. Can anybody help? or know were I could get the inverter checked out. OR do I just wire it into the 30A breaker ?
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SteveW
Elder Statesman
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Post by SteveW on Jan 22, 2006 21:18:39 GMT
Uzzy,
This isn't going to help but our club had exactly the same problem with an inverter equipped mill. The solution was to swap out the inverter for a simple motor drive (Ug!).
Re your problem: These things are switching systems and can generate a lot of electrical noise back down the mains wiring which would cause considerable interference if not stopped by a filter circuit.
If this noise were not filtered it would also cause the unit to loose its CE certification which means it can't be sold in Europe.
The filter circuit is something like a series coil in each leg of the mains wiring and a couple of capacitors to ground to shunt the 'noise' to earth. This leak to earth is what the RCD sees as an error (un-safe) condition and trips out.
QED.
I saw this sort of problem with American kit I used to use at work.
The solution was generally to use a higher leak rated RCD. Whatever you do DO NOT float the earth connection to get around it because the shut capacitors effectively connect live to chassis.
In this context the RCD is something of a nice to have. If your system is correctly installed and everything is bonded to ground the fuse should be sufficient to protect from direct live to ground faults but there could still be a big bang. This is actually a very complex area of circuit impedances hence my "correctly installed" bit.
Consider a separate supply, possibly with a suitable higher rated RCD aimed at protecting equipment and not people.
Another point with RCDs is that they need testing routinely. This means things like correct tripping current (pos & neg cycles) and within defined time-to-trip limits.
Modern switch mode power supplies (& maybe arc welders) can draw asymmetric currents on each cycle which can polarise the RCD core and compromise operation.
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jackrae
Elder Statesman
Posts: 1,333
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Post by jackrae on Jan 23, 2006 7:18:19 GMT
First thing to do is ensure you have not inadvertantly crossed the earth and neutral wires or that the neutral is contacting the earth wire.
In your wiring you may have inadvetantly used the equipment structure to form part of the circuit.
19mA seems quite a sensitive unit, the general standard for domestic protection systems being 30mA.
Whatever you do, do not instal a 100mA RCD since it offers inadequate personal protection.
Always bear in mind that safety devices which trip are doing so for a reason. It may be a pain in the butt but you need to identify where your problem lies. Simply taking avoidance measures like bypassing the RCD is not the way to go. Better to be alive with a dead invertor than be dead with a working one.
When I was an apprentice we had the saying :- "It's the volts which jolts but the mills which kills"
Jack
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Post by Malcolm on Jan 24, 2006 21:19:17 GMT
It might be worth checking the current at which the RCD trips. I had a case recently where a 30mA RCD tripped at 19 mA. A similar replacement also tripped at 19 mA. If there is a standing earth leakage current from other equipment the additional small leakage from the inverter might be enough to cause a trip.
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Uzzy
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Posts: 153
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Post by Uzzy on Jan 24, 2006 22:15:08 GMT
Thanks for all your replies, I have now disconected the earth from the power in side and it does not pop the breaker but there again my machine is still dead although the lights on the inverter come on. Any suggestions?
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SteveW
Elder Statesman
Posts: 1,383
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Post by SteveW on Jan 25, 2006 1:37:27 GMT
Uzzy
My suggestion is:
RE-CONNECT THE GROUND/EARTH WIRE BEFORE THE GRIM REAPER GETS TO EXPLAIN TO YOU IN PERSON WHERE YOU WENT WRONG AND DON'T DISCONNECT IT AGAIN. EVER!
REMEMBER: ELECTICITY IS OUT TO GET YOU!
With the earth disconnected on the mill you can easily find 230volts between the chassis and other earthed kit.
A good move in any workshop is to bond all exposed mains powered metal things together in addition to the main lead. Bonding is a second defence to loosing an earth connection on one unit. Basically if the whole room floats at 230volts (i.e. the equi-potential zone) you are sort-of safe(ish) until you reach out of it to the real grounded world (see reaper comment above).
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Post by catgate on Jan 25, 2006 19:22:33 GMT
It could be as simple as the wrong MCB type. You need one that is refered to as a "C" type. It is slower acting. There is a "D" type but that is a bit extreme. Your original set up may have been OK with one of these MCBs. I recently went through this myself with my Troublesome Triumph, reported on during the middle of '05.
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jackrae
Elder Statesman
Posts: 1,333
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Post by jackrae on Jan 25, 2006 23:19:45 GMT
Please note that an MCB offers you no personal protection from electrocution and only protects the system from electrical overload (caused by either a short circuit or you trying to suck too much power out of the wall)
For protection against faults liable to cause electrocution you definitely require an RCCB or (to us used to the pre European era) an ELCB. These devices sense the imbalance between the current flowing to the end device (eg a motor) down the live wire and the return current coming back from it up the neutral wire. The difference is either the leakage to earth (due to a faulty device or insulation) or the current flowing through your body to earth (if you've grabbed hold of the live wire).
Note that a simple mis-wire of connecting the neutral to earth should also trip an RCCB even without the live wire connected. This is caused by the slight potential difference between the neutral and earth wires causing a curent to be sensed by the device.
Where you have lots of metal machinery around you really must use an RCCB to cover for the possibility of an electrical fault. Although all machines must be earthed the RCCB continues to provide adequate protection in the event of making contact with juicy bits. Portable tools get away without earths if they are certified as being double insulated.
There are old electricians and there are bold electricians but there are very few old and bold electricians.
Take care and be safe
regards Jack
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Post by houstonceng on Jan 26, 2006 0:40:22 GMT
Uzzy
A lot of good advice in the replies about MCBs (aka "fancy fuses" that stop the wiring going up in smoke) and devices variously called over the years ELCBs / RCCBs / RCBs / GFIs / RCD (aka "fancy devices" to stop you going up in smoke if you happen to cut through a wire or touch an exposed live (or neutral) contact). Bottom line is that a 16amp MCB should be ok and a 30ma fault trip current GFI/RCD should be ok to run an inverter (more correctly termed a Variable Frequency Drive). ref Jackrae's & Malcolm's notes. If your RCD pops at 19ma it definitely sounds like the wrong type for your house/workshop wiring. I'd only expect to see one with that rating internal to equipment or dedicated to a single load. There again, 100ma is too high for adequate protection in a domestic / workshop environment.
I have a Eurotherm VFD on my mill, connected to a dedicated MCB which is, in turn, fed from a 30ma fault trip RCD (the latter protects the majority of the sockets in my house and workshop). I have had only two isolated instances of "popping" the RCD caused by the mill. One was caused by the cheap transformer supplied with the auto-feed (240 to 115v) which went "short circuit" - because it was under-rated for the job - now replaced by a "site transformer". The other cause was a bit of supplier's bad internal wiring. I must have disturbed it when emptying the suds tank (Power off) and it shorted to the metalwork when I reconnected the power.
I agree with most everything said about having an effective earth. Stress effective ! Bonding all your machines is, IMHO, going a bit too far and may, in some instances, lead to popping your RCD. If you must work on "live equipment" without the earth connected - and some of us have had to do this a number of times as a fault-finding mechanism in a lifetime of "electrickery" - then only use one hand and make sure you have some decent rubber soled boots on. Oh ! and make sure you tell the distaff side, helpers, onlookers, etc, NOT to touch you whilst you are so doing - otherwise it might be "two for the price of one" at St Peter's gate.
It's a bit difficult to give a definitive answer on "what's wrong" with your set-up - somewhat like when my friends and family used to ring up and ask what was wrong with their TVs - as I used to say "sorry I don't have a video phone so I can't see your TV picture". I really need to know :- What make of VFD have you got ? What size of motor ? Was the set-up "pre-wired" or a DIY conversion ? Have you an EMC filter internal/external to the VFD? What's the wiring diagram of your set-up ?
In fact as much info as possible - failing an actual visit - including wiring diagrams if possible. For example, I assume that the motor is connected directly to the VFD and not through any contactors, switches, etc., and that it's a 3-phase type in delta configuration, but, if I've learnt anything about diagnostics in electronics/electrickery its, "Don't assume anything".
Another thing mentioned was the RFI (Radio Frequency Interference) filter or EMC filter as it's usually now called. Many of these have delta capacitors (one across L & N and one from each of L & N to E). These usually cause problems with RCDs if not "low leakage" designs. Some VFD manufacturers recommend not having an EMC filter if you have an RCD or, if you need an EMC filter, not having an RCD.
The final thought is that if you actually got lights on the VFD but no revolution of the motor, I fail to see what the MCB has to do with the case - unless it popped when the motor started. Again, more info required.
Deja vu ? When this group was sending E-mails to each other rather than being web-based, I'm sure we went through a similar corresponence with another "good buddy". Maybe I'm wrong !
Andy
There are many old Chartered Electrical Engineers and there are many bold Chartered Electrical Engineers but there are few old and bold Chartered Electrical Engineers.
So - -
I must state that :- 1. Electricity carries with it a danger of death. Therefore, if you don't feel confident with it, you should seek appropriate professional assistance. 2. This explaination is offered to you as a friend in order to assist your basic understanding of the stated problem. It in no way constitutes a design solution or installation instructions. Nor can any of this explaination be considered as professional advice given by me. 3. I accept no responsibility for damage to property or injury to persons as a direct or indirect outcome of this correspondence.
(Well you've got to be careful that can't be sued these days !)
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Uzzy
Hi-poster
Posts: 153
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Post by Uzzy on Jan 26, 2006 20:54:24 GMT
Thanks for all your comments. Andy at HOUSTONCENG if you send me your email address I will forward you all the details maybe we can work this out.
Regards Ian
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Post by Malcolm on Jan 26, 2006 21:27:36 GMT
I second the above remarks re safety. As someone once said about electricity: You can't see it, you can't hear it, you can't smell it and you daren't touch it!
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Post by ukjimoo on Feb 6, 2006 12:08:24 GMT
Hi Uzzy I had exactly the same problem with a Siemens inverter. As soon as i switched it on the 30mA RCCB tripped. I found that cutting out the previously mentioned capacitors cured the problem and did not affect the operation of the unit. Only problem is that it now plays havoc with any LongWave radio reception within a 10metre radius of it Jim
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Post by houstonceng on Feb 10, 2006 19:33:58 GMT
Guys
During our attempts to get his Siemans Micromaster 420 inverter going, Uzzy and I have hit the proverbial "brick wall". Missives from me to Siemens have been of no avail - except a suggestion that we need to gain access to the Parameters and Fault-codes for better diagnostic aid. A conclusion that we had already arrived at.
The SDP supplied with the unit cannot do this, so - - - - - - -
- - - Has anyone in this Group got one - or more - of the following which they would be prepared to lend us - or sell for a reasonable fee ? :- A Basic Operator Panel (BOP) An Advanced Operatot Panel (AOP) A PC to Inverter Connection Kit + S'ware CD normally supplied with Instruction Manual.
Andy
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Post by ukjimoo on Feb 13, 2006 14:15:51 GMT
I have been down this road already and to no avail. My inverter is also a micromaster 420. I have been in touch with siemens and the upshot of it is that these units are not designed with domestic installation in mind and they do have inherant leakage to earth. There is a parameter that you can change to lessen this leakage and it does cure the problem, but the motor makes an unbearable noise. The sound of square waves i think. As i mentioned in my previous posting, i cut out the 3 large capacitors inside the unit. This was suggested by the techy at Siemens on the understanding that it was an UNOFFICIAL suggestion. Since removing the capacitors i have had 2 years of trouble free, variable speed running. Only problem is with any AM radio in the close vicinity.
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Post by stuboy on Jan 25, 2015 18:19:40 GMT
Hi Guys Just come across your excellent thread being a Micromaster 420 owner. I have exactly the same problems as you have had. I won't bother going to the unhelpful Siemans, when i spoke to them they had never heard of Mach3! I also pulled mine apart last night to find 4 of the 6 electrolytics that look like secondary smoothing had all popped, worth checking if your taking your apart. I might experiment putting some smaller C's in instead of the ones that are doing the filtering and see if there is a compromise that works. It leaks 14mA by the way, but clearly on switch on its a heap more, hence or 30mA RCCB's going.
Regards Stuart
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Post by houstonceng on Jan 25, 2015 20:08:26 GMT
Hi Stuart
Uzzy's problem transpired to be an inverter which was too small for the motor - a misunderstanding of both ratings by Uzzy. I visited him and we ran the inverter from the house mains to use the 30mA RCD then reset the parameters with the control panel he bought extra to the inverter. We were then able to turn the motor over, but it tripped the over current when we attempted to increase the speed.
I believe he gave up Model Engineering for a time and decided to concentrate on another of his hobbies.
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Post by stuboy on Jan 25, 2015 20:27:43 GMT
Are you saying it ran every time ok from normal 30mA protected supply? I found the first time you plug it in it nearly always trips, the second i assume some caps have charged and it switches on. I was going to change the Caps for something half the size and see if i can up the impedance enough to stop it blowing. I have 8mA of leakage from everything else attached to the trip so I have to get it to less than 20mA to keep everything happy. Regards Stuart
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Post by Roger on Jan 26, 2015 5:39:54 GMT
I had a similar problem with a Control Techniques drive.
Their manual states the following... The drive is supplies with and internal EMC filter capacitor installed. If the input voltage to the drive is supplied through an ELCB or RCD, these may trip due to the ground leakage current.
It then goes on to explain how to disconnect that internal capacitor.
Your drive may have a similar setup.
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Post by houstonceng on Jan 26, 2015 7:01:01 GMT
Yes. It ran OK first time from 30mA RCD. Uzzy's WS was fitted with a 25mA RCD to allow differential tripping. That was too low. As I said, we didn't get to run it fully as it was, IIRC, a 1/3hp inverter and the 3 phase motor was a 6 pole 1/2hp, so the over current protection on the inverter operated as soon as you tried to adjust speed.
Siemens inverters were available without the EMC filter, in case they caused a problem. They were said to require at least a 30 mA RCD and were for "industrial" application.
I have a Mitsubishi 2hp inverter on my lathe and have no problems running it on a dedicated 30A supply from a 30mA RCD.
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Post by stuboy on Jan 26, 2015 21:38:42 GMT
Well I tried replacing the 0.1uF with 15nF and the 47nF with 22nF to no avail still pops the breaker, will try smaller again and report back!
I replaced them all with 15nF and it still popped. Took them out of circuit and it switched on ok. Taken back to workshop and plugged it in, switched on with motor attached and its popped the RCD again.
Well I've done some more reading and it looks like quite a few people that try and use a VFD in their garages have the same problem, my theory is that the extra capacitance on some circuits makes them much more prone to tripping. When i tried it on my other ring in the house it didn't trip once.
So I cycled over to Screwfix and purchased a garage consumer unit. Then re-wired my main consumer unit so the garage feed is directly after the main switch, thru a 40A RCB and before either of the RCD's. The garage then has a main switch RCD a lighting circuit and 2 power circuits. I've put all the router stuff on one circuit. Wired it all up and tested it, then hey presto i can turn the drive on and off to my hearts content :-) Put original filter parts back in ie 47nF and 3x 100nF and all still works fine. I will chalk that one up to experience, next to re-install the full filter circuitry and see if i can still switch it on. Regards Stuart
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