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coillah

Wed Apr 14 2010, 03:46AM

Registered Member #1517 Joined: Wed Jun 04 2008, 06:55AM
Location: Chico CA
Posts: 304

I need some tips, or a website to go read for power distribution design techniques. Specifically I am trying to build a power distro unit using SSR's for a project. I am working with multiple loads in the 10A range apiece. I would like some pointers on good electrical engineering practice, what I should look out for, etc.

Thanks in advance!

Steve Conner

Wed Apr 14 2010, 11:24AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

What kind of power? AC? DC? What voltage/current? Where? The techniques used are different. Compare the power distribution system in an automobile, aircraft or ship, a data center or telephone exchange, to the one in your home. Different philosophies, different bodies of information, different ideas of what constitutes "good practice", you need to choose one.

radiotech

Wed Apr 14 2010, 05:52PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

SSRs provide isolation between i/o for control but not seperation required by codes between power sources feeding common apparatus.

You cant apply a lock to them nor see if the switch is open for safety.

Here are couple of types. The big blocks are good for installation into machinery for retrofit. The small one is a P&B module used in a TDC (Total Distributed Control) automation computer used in a power generating station.

coillah

Thu Apr 15 2010, 12:21AM

Registered Member #1517 Joined: Wed Jun 04 2008, 06:55AM
Location: Chico CA
Posts: 304

Steve McConner wrote ...

What kind of power? AC? DC? What voltage/current? Where? The techniques used are different. Compare the power distribution system in an automobile, aircraft or ship, a data center or telephone exchange, to the one in your home. Different philosophies, different bodies of information, different ideas of what constitutes "good practice", you need to choose one.

Thanks Steve. Here are the details I left out:

- PDU controls power to two AC loads, a roughing pump and a diffusion pump for a high vacuum system, the SSR's have been selected already for this portion of the project
- apart from the controlled loads there are at least 3 other loads eating AC power, one is a motor
- the main power source is a 220VAC (two hots, one neut, and one ground)
- current plan is to take the two hot's and use them separately to power the loads individually
- plan to include two breakers at the entrance, each responsible for one hot line (should each load have its own fuse as well?)
- all in all, the loads add up to 46A, we should have a 50A breaker on the line before the wall outlet (or 2x25A breakers, need to double check this with my notes)

I need to know the best practice for splitting up the hot lines to go to each individual load, ie. terminations, where things should be grounded. In general, all the stuff they don't teach the electrical engineer in school anymore. Honestly, there is no such thing as a practical EE course at my school anymore, nearly all the professors only deal with stuff past a zener regulator... go figure.

I try to ask a technician, or electrician, but most of those guys just give you shit for not knowing, "oh, but aren't you an engineer...?" you know?

Anyways, if anyone has a good book or resource on the web (wikipedia doesn't seem that helpful right now), I'd greatly appreciate it. And please don't tell me to quit because I don't know this stuff already. I need to learn it because this project needs to succeed. Please help.

BTW, I have checked my library and picked up a few books, but most are dated, and I haven't found anything which directly answers any questions I have.

Nik

Thu Apr 15 2010, 03:02AM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

Im an electrician and the one thing i can tell you is breaker sizes (at least in canada), we never load a breaker to more then 80% of its trip rating. So you should probably use a 60amp not a 50 amp breaker. This prevents nuisance tripping and lengthens the life of the breaker. You should also size your wire accordingly so #4 awg wire unless you get higher temperature insulation then you can go down to #6.

radiotech

Thu Apr 15 2010, 04:39AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

As an EE, you could look up the NEC or CEC codebooks depending on what country you live in. Then check local codes to see what permits you have to take out to get your PDU and connections inspected to protect your liability in case of fire damage if the installation is flawed. As to getting an licensed electrician to help you, the issue there is without a permit his license (and surety bond)could be could be pulled for violation.

From what you say, It seems that your project is a self contained unit, or assembly complete with control system, that connects to a 240/120 signle phase source, like a 60 amp breaker and has that breaker as the shutoff.

A lot of packages like this are manufactured for the chemical or waste management fields and have a single approval label stating the whole machine may be hooked up just like a stove.

Since you are not an electrician, you may read the code rules to see how the individual regulations apply the installation of wires and devices. That wont help, but books like the "American Electricians Handbook" may show some of the practical aspects of cables, conduits and work practices.

Think about something like an elevator, all the controls for the motors are housed in single assembly, approved for intalation, and brought to a building and attached to the power , hoist motor, and floor auxillaries.

It would be nice if you could look at some assemblies like this.
All big institutions have them.

A lot of them use "Panduit" raceways to organize wires.

coillah

Wed Apr 21 2010, 10:39PM

Registered Member #1517 Joined: Wed Jun 04 2008, 06:55AM
Location: Chico CA
Posts: 304

I had a "non-licensed" electrician look over my work. It appears that everything is good! The only thing missing was a mains breaker outside the distribution box enclosure. All the gauges and whatnot were sized correctly and the circuit itself was done nicely. Later that day I was working with someone on an X-ray machine and noticed the PDU inside the machine was doing exactly what I had planned for my vacuum chamber.

Pretty cool huh?

Anyways, thanks guys for the help. If you have found this thread and want to know more about what I ended up doing, just message me. I am going to try and submit this project to hackaday and this website.

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