Oil Switches

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Anonymous Poster	Oil Switches 09/13/2010 8:06 AM
	We have a number of oil switches that we have been told we can not switch live anymore. Why is that? We've been using them for years without trouble! It now causes many problems as we have to switch off more of the system just to use one switch.
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PWSlack Guru Join Date: Jan 2007 Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on. Posts: 32175 Good Answers: 839	#1 Re: Oil switches 09/13/2010 8:22 AM
	What make are they? Are they EEx o? Where are they installed? What rating are they? Where has the prohibition come from? What is the accompanying explanation? __________________ "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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Anonymous Poster	#2 In reply to #1 Re: Oil switches 09/13/2010 9:12 AM
	Several are Reyrolle(20), Ferguson Pallin(3) and a Metro Vic Some of the Reyrolle are Ex The prohibition came from the local inspector. Unsafe to operate live! Why they've worked for years without fault.
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PWSlack Guru Join Date: Jan 2007 Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on. Posts: 32175 Good Answers: 839	#3 In reply to #2 Re: Oil switches 09/13/2010 12:42 PM
	OK. EEx o is an acceptable method of explosion protection in Zone 2. Are these switches installed in Zone 2? What is the reason for the prohibition other than <...unsafe to operate live...>? What reasons did the inspector give to substantiate the judgement? Has the oil run out and not been refilled? Why are the switches still there? Why can't they be replaced with EEx de ones? What background and clout does the inspector have? __________________ "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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Anonymous Poster	#4 Re: Oil Switches 09/14/2010 4:32 AM
	The Ex switches were bought second hand I think (they don't need to be). The inspectors report (now I've seen it) says they are manual switches and not to be operated under load. They've given good service and now aren't safe!
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TonyS Guru Join Date: Aug 2010 Location: Resting under the Major Oak Posts: 4347 Good Answers: 181	#5 Re: Oil Switches 09/14/2010 7:26 AM
	Dependant Manual Operation switches (DMO) are regarded a dangerous due to the fact the closing speed of the contacts depends on the speed the switch handle is moved. You could slowly close a switch, which while under load or fault will cause an arc, generating gasses that can lead to an explosion. I've closed old (1940's) Reyrolle Ex switches on to load and they fight back as the contacts close! You have to be quick and decisive when operating a DMO switch. You could also change your mind while operating the switch, the contacts touch and start to push back so you let the switch open slowly. Again ARC, GAS, BANG! The bigger the switch the slower the operation due to the mechanical advantage needed to close the contacts. Maintenance of DMO switch's is also a big consideration, not many people know how to look after them now. It all comes down to the speed and positive action of modern circuit beakers. I know it's a big job but get rid of any DMO switch they are dangerous! __________________ The reports of my death are greatly exaggerated.
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klearzen Power-User Join Date: Jun 2010 Location: St Louis MO USA Posts: 224 Good Answers: 7	#6 In reply to #5 Re: Oil Switches 09/14/2010 12:59 PM
	Tony GA .... Thank you for sharing and informing us on what is a (real world) serious concern. I myself ... am an old sailor with some industrial maintenance experience, now in a supervisory role, and just beginning school in the electrical trade. All your previous experiences shared, will add value to my training. Again thank you. Ray __________________ klearzen
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TonyS Guru Join Date: Aug 2010 Location: Resting under the Major Oak Posts: 4347 Good Answers: 181	#7 Re: Oil Switches 09/15/2010 4:57 AM
	I'm just glad someone else appreciates the danger of these things. Over the years I've come across some beauties, my favourite has got to be a 3.3KV knife switch isolator for a 400HP motor it was linked to a DMO oil switch. There were no interlocks to stop anyone opening the knife switch under load! Next to it was a cubical with oil filled re-wireable glass fuses, the cubical wasn't even locked! That particular switch room got the nick name "suicide ally". __________________ The reports of my death are greatly exaggerated.
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Anonymous Poster (2); klearzen (1); PWSlack (2); TonyS (2)

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