Forums
New posts
Search forums
What's new
New posts
New media
New media comments
Latest activity
Media
New media
New comments
Search media
Members
Current visitors
Log in
Register
What's new
Search
Search
Search titles only
By:
New posts
Search forums
Menu
Log in
Register
Install the app
Install
Main Forums
Electrical Inspection & Testing Forum
I.R Test on an Isolated Motor on a live working Industrial Machine
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Reply to thread
Help Support Talk Electrician Forum:
This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Message
<blockquote data-quote="Sidewinder" data-source="post: 416195" data-attributes="member: 9512"><p>Q1.</p><p></p><p>OK, yes you can IR @ 500V, the live conductors are isolated from the rest of the machine, thus here is no way for the voltage to feed back into the remainder of the machine via the phase lines to the motor.</p><p></p><p>The IR tester whilst generating 500V between the probes, has negligible current, the spec on my Fluke is 1mA @ 500k Ohms load resistance.</p><p></p><p>Thus with the machine correctly designed and built the bonding and earthing of the machine will ensure that there will be negligible potential across the machine.</p><p></p><p>Just think, in the event of an earth fault it would be required to keep the potential differences very low to ensure operation of the protective devices, and that would have a LOT more than 1mA of current flowing.</p><p></p><p>The test current, will flow between the lowest resistances which are likely to be the faulty motor, there is technically no current path down the live conductors past the isolator anyway.</p><p></p><p>There will be a connection from the motor earth back to the main machine earthing system, but, where will the current flow path be to cause any current to flow down a path to even be conducted through these items?</p><p></p><p>Q2.</p><p></p><p>How can the test voltage appear anywhere on earthed metal work elsewhere on the machine, it would need current flow, see above, what would be the current path to cause the earthed metalwork to rise to any sort of potential above that of earth?</p><p></p><p>Q3.</p><p></p><p>You will probably find that the official OEM guidance is to earth both sides of the thermistor at the motor earthing connection. That was certainly what our instructions said when I worked for a motor OEM.</p><p></p><p>However, again, think about where the potential will exist and the current path.</p><p></p><p>Is there anything else...</p><p></p><p>LOTO, safe working, making sure that you can’t be injured by anything else on the machine if it were to go into failure, or during normal operation. Do a suitable and sufficient risk assessment, and a method statement and stick to them, you don’t need necessarily to write anything down, just do it mentally. Engage in dynamic risk assessment &amp; mitigation as you work.</p></blockquote><p></p>
[QUOTE="Sidewinder, post: 416195, member: 9512"] Q1. OK, yes you can IR @ 500V, the live conductors are isolated from the rest of the machine, thus here is no way for the voltage to feed back into the remainder of the machine via the phase lines to the motor. The IR tester whilst generating 500V between the probes, has negligible current, the spec on my Fluke is 1mA @ 500k Ohms load resistance. Thus with the machine correctly designed and built the bonding and earthing of the machine will ensure that there will be negligible potential across the machine. Just think, in the event of an earth fault it would be required to keep the potential differences very low to ensure operation of the protective devices, and that would have a LOT more than 1mA of current flowing. The test current, will flow between the lowest resistances which are likely to be the faulty motor, there is technically no current path down the live conductors past the isolator anyway. There will be a connection from the motor earth back to the main machine earthing system, but, where will the current flow path be to cause any current to flow down a path to even be conducted through these items? Q2. How can the test voltage appear anywhere on earthed metal work elsewhere on the machine, it would need current flow, see above, what would be the current path to cause the earthed metalwork to rise to any sort of potential above that of earth? Q3. You will probably find that the official OEM guidance is to earth both sides of the thermistor at the motor earthing connection. That was certainly what our instructions said when I worked for a motor OEM. However, again, think about where the potential will exist and the current path. Is there anything else... LOTO, safe working, making sure that you can’t be injured by anything else on the machine if it were to go into failure, or during normal operation. Do a suitable and sufficient risk assessment, and a method statement and stick to them, you don’t need necessarily to write anything down, just do it mentally. Engage in dynamic risk assessment & mitigation as you work. [/QUOTE]
Insert quotes…
Verification
Post reply
Main Forums
Electrical Inspection & Testing Forum
I.R Test on an Isolated Motor on a live working Industrial Machine
Top