Interesting thread. I've learned a bit about SSRs myself.
As FYI, the black wire is hot in 110v USA wiring, so that's the one switch with the relay or SSR. (White is neutral, which is ultimately wired to the ground bus bar in the panel.) Of course, breaking the neutral will turn the device off, but it leaves it in a hot state that is misleading and hazardous.
Cheers, Richard
Oops, It's been a long time! Black, I knew that. :)
Mnemonic -> black == death
Best regards, Spehro Pefhany
In a some cultures white is the color of death. So you may run into trouble with this if you let the chinese assemble your stuff. ;-)
Over here the hot wire is brown, but the switched hot is black.
Another consideration is current capability. Often to boost current handling an SSR is used in parallel to the relay, but with separate control. The SSR is turned on first, ideally at the zero crossing and makes the connection, eliminating arcing on the relay. The relay is turned on second to handle the full load and reduce the heat loss in the SSR. On shut down the opposite is done.
Scott
And illegal per the National Electrical Code.
There is, sometimes, too much nannying going on. In order to learn the practical aspects it is sometimes necessary to take a step that has some risk. However, I would hope that the tutorial staff would be able to advise the OP what risks he was facing in doing this project and the risk mitigation measures that would reduce the risk to an acceptably low level (see ALARP). Otherwise, when these students get to industry they are un-prepared to make decisions about system risks.
Kind of related to this current thread:
This came as a shock to me. A few years back, I used zero cross SSRs to control my pool pump via a timer. According to this document, I should have used a random SSR instead of zero-cross---- I'm not totally convinced yet this article is right.
ie. I believe it makes sense that the current will be high on an inductive load at switching transient---but, it seems as though they are more interested in saving the life of the SSR--as opposed to the inductive load (a 1-2hp motor in my case). My pool guy said, "don't put a timer on it--let it run 24/7--otherwise I'll be out in a year or so replacing your dead pump motor". But, I thought 'hey, if I switch at zero, it can't hurt the motor'. So far I've had no problems with the setup at all.
Did I do the right thing? with respect to the motor? I'd rather replace a $30 SSR than a $350 pump.
Thoughts?
Paul
This article relates to energising tramsformers not motors. For all practical purposes it makes no diference when you energise a motor.
:-)) In that case you'll probably connect them all together and don't even bother to find out why it doesn't work.
I think you and I are on the same page. I wish to *TERRIFY* OP into asking instructor(s) WHY ;)
Have something to add? Share your thoughts — no account required.
Ask the community — no account required