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Have a look at the following: http://www.tew.co.uk/index.php?option=com_content&task=view&id=18&Itemid=83 for the UK or http://www.tew-eng.de/index.php?option=com_content&task=view&id=18&Itemid=83 for Germany I have no connection with the company apart from using them for a quotation to...

Thanks Warpspeed, that makes good sense. Olavurthomsen, It sounds an interesting problem you have there! I can well imagine it hapenning, but not sure of a cure. Maybe a large resistive load connected at switch-on and then turned off via a timer would absorb the transients, or MOV's connected...

I am aware of the potential problems of using long cables on the output of VFDs with the IGBT output switching causing a high voltage standing wave, stressing cable and motor insulation. Also problems caused by common mode noise from such systems. Are the same problems likely with...

Crouzet are a long established company that do a good range.http://files.engineering.com/getfile.aspx?folder=6be0c46a-44a2-4714-bb85-76ed20f88388&file=Crouzet.pdf

When I was involved with electric furnaces years ago, we fitted flow switches in the water return pipes from each electrode. When the flow rate dropped below a predetermined level, it signalled an alarm. Simple and effective.

The Reyrolle name is now used for the protection side of the business. http://www.reyrolle-protection.com/index.php

Some VFDs do not like driving into an open circuit. You need to talk to specific vendors if their drive is suitable or not. My preference is to put the contactor at the input to the VFD and an interlocked isolator adjacent to the motor.

Thanks Scotty, I was thinking more of the dip on the switchboards affecting other equipment when using a weak supply such as a generator. Contactor mfrs often quote figures of acceptable control voltage before they drop out. Voltage dips can cause re-strikes on sodium lighting etc. I was...

When doing calculations for voltage drop when motor starting, I have always used figures of 20% at motor terminals or 15% at the switchboards as maximum allowable. Can anyone tell me if there is a British Standard that actually defines the allowable voltage drop and time periods when motor...

Common in the UK Triple pole & Neutral. Usually 400V, where you want a mixture of 400V 3ph and 230V single ph loads from one board.

Thank you Keith. I did notice that the OP wanted a symbol for a SLD, in which case my spider would lose another 7 legs! I vaguely remember borrowing this symbol from one of the motor manufactures literature. I have been in the electrical Engineering game for over 25 years and spent 7 at...

This is what I use. Not sure where it originated from.http://files.engineering.com/getfile.aspx?folder=133beb3d-008a-45c8-b736-556e770c2e01&file=motor.pdf

Stuart, I think this is the Siemens book that ScottyUK is referring to. I have found it to have some very useful references in there, despite its bias to Siemens products. http://support.automation.siemens.com/WW/view/en/28813929 ScottyUK, Didn’t Enron become NEL, then Carron Engineering...

For the jobs that I have been involved in at refineries, the storage tanks have always had separate earth pits / rods, the number of which depended on the size of the tank. Not connected to the main earth grid. I’m not sure of the reasoning behind this, just an observation I have made. I’m...

I have also used P&V, but as with all these database systems, you have to be diciplined in the way you name things. Uper case, lower case, full stops etc. It can be easier for the user to add a new part number than it is to search for an existing item. Restricting users from creating new...

We were considering them for use in distributed motor starters but knocked them back when we discovered that only two of the three poles were switched. Matt

In many systems that I have worked on, the machines 24V psu would have the 0V rail connected to earth. This is effectively commoning up all the 0Vs anyway. Matt

The way that I would do this is to take the 24V PLC supply through clean contacts on the machines. Can you disconnect the machines internal supply from the start PB and limit sw? It depends on the spec of the PLC input card. If they are individual isolated inputs, you could probably take the...

Thanks for the quick and helpful answers. Matt

It varies depending on size, shape and surface texture of the item in question. As a general rule of thumb, we put the warning label on any equipment that may reach above above 60 degC. VFD heatsinks for instance. Matt