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Old 08-18-2012, 11:11 PM   #1
krazydave
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Default Help me scrutinize my control panel wiring diagram

Working on building a NG fired brutus 10 type system and am just getting around to working on a wiring diagram for my control panel. The system will have three Honeywell VR8200 valves, two controlled by Auber SYL-2362 PID's. The boil kettle will be controlled via a switch on the control panel (no need for a PID there).
I've also implemented P-J's e-stop and two alarm switches for the PID's that will control a 24VAC flashing buzzer.

My main questions are:
-Do I have fuses where I need them, and should I put one on the gas valves?
-Am I running the wiring efficiently enough by running some stuff in parallel?
-Do I actually have these PID's wired correctly for PID relay control, with J2 as my temp alarm?
-Should I use that many terminal blocks, or does anyone have any better ideas?

Thanks in advance!

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Old 08-21-2012, 07:21 PM   #2
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Maybe have a fuse at least on the hot primary line to the transformer and optionally on the output. Usually industrial panels I've seen, the 'neutral' on the transformer output is also grounded to prevent the secondary voltages from floating with respect to ground.

For the e-stop maybe just using the main power switch would be better? The way it is the button relies on the GFCI being functional to trip, which yes it should be, but in a situation where the e-stop is needed you don't want to find out the GFCI is failing to trip for some reason.

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Old 08-21-2012, 10:28 PM   #3
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Thanks for the response porcupine!

Question regarding the transformer neutral to ground. I plan on grounding the enclosure, is it safe to assume that the transformer being grounded as it's mounted to the backplate that's also grounded, is sufficient enough to stop floating voltages? Or is the neutral and chassis of the transformer isolated?
I was going off of Kal's plans, amongst others and thus far haven't seen any mention of grounding the secondary neutral. Googling it gives me plenty of results on home and commercial transformer wiring where they do this, but I'm not finding much in terms of lower voltage control panel transformers. I'm curious how much of an issue it would really be...

I agree on the e-stop\GFCI issue, however I think the true function of an e-stop is to kill all power throughout the system. P-J found a pretty good solution for this with his GFCI usage. However, I will also have the main power switch there should the GFCI fail to trip from the e-stop.

As for fuses, any thoughts on what size\type of fuses I should use for the transformer lines?

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Old 08-22-2012, 01:03 AM   #4
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Fuse size for the transformer would depend on two things, the VA rating of the xfmr and the xfmr impedance. Basically at the minimum a short circuit on the secondary side needs to blow the primary fuse, and ideally if the xfmr is overloaded it should blow as well. Sometimes people fuse both the primary and secondary.

I'm not sure if any CPT's control power transformers have any leads of the output grounded to the chassis. I would guess probably not. Where I work we always show grounding one of the power leads out of the CPT but often see it missing in the panels when they are built.

An e-stop ideally needs to shut down all powered equipment. However normally e-stops are hardwired so that they do not depend on any part of the control system functioning properly. I would consider the GFCI part of the control system in this case. I believe on a GFCI a neutral to ground short is supposed to trip it as well.

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Old 08-22-2012, 03:42 AM   #5
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@porcupine I agree with your feelings on P-J's GFCI E-Stop configuration that seems to be ubiquitous on this forum. This has always bothered me. Though it is clever, it intuitively seems dangerous, especially considering all the potential points of failure. At the moment, I can't quote any specific NEC code that would prohibit this. A ground conductor shouldn't be considered a current carrying conductor.

And, in general, E-Stops should open a circuit--not close a circuit. If you are really set on tripping the breaker it should be done with a shunt trip breaker that is specifically designed for this purpose and doesn't require grounding the hot conductor.

As an alternative, you could use a simple contactor (appropriately rated) to switch your incoming power and a normally-closed Mushroom pushbutton to drive the contactor coil.

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Old 08-22-2012, 04:40 AM   #6
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Quote:
Originally Posted by FastTalker

As an alternative, you could use a simple contactor (appropriately rated) to switch your incoming power and a normally-closed Mushroom pushbutton to drive the contactor coil.
I have though about this, but as I am renting the house I'm in currently, I didn't want to install a permanent housing for the contactor. I do agree though that this would be the proper way to go and will likely do that once I'm in a home I own again.

@porcupine, I'm on my phone currently, so I don't have reference to the exact transformer I purchased. As soon as I get on my computer though I'll see if I can find the full specs of it so we can figure out the fuse sizes.
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Old 08-22-2012, 02:26 PM   #7
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Good points all around. Normally if I'm using a breaker with 'side pockets' that support shunt trips, I'd use a undervoltage release rather than a shunt trip for any critical application, so that the 'fail safe' is to trip the breaker. The downside is that on a power outage the breaker trips as well. Or I've seen normally closed maintained pushbuttons that when you press it stays pressed in, and you twist the button then to release it again. I'm sure Allen Bradley has these though just putting the AB logo on something seems to increase the price about $70.

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Old 08-22-2012, 07:38 PM   #8
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Here's the transformer I bought for the control panel. It's a 75VA transformer, not certain of what the impedance is on it though.
http://www.pexsupply.com/Honeywell-AT175A1008-Foot-mounted-120-208-240-Vac-Transformer-w-9-in-Lead-Wires-75VA-11016000-p

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Old 08-22-2012, 08:11 PM   #9
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For that I might run a .75A or 1 amp slo blo fuse on the primary side. 75VA/120V = 0.625A on the primary side, then I think you're allowed to go up to 125% of that in the overcurrent device, which would be .78A or so. It's just without any fuse on that transformer if it has a fault or the secondary is overloaded the xfmr could get very very hot.

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Old 08-22-2012, 09:06 PM   #10
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Sounds good. I'll go pick some up. Thanks again for the advice and taking the time to look it over!
Hopefully I'll be able to get to building this thing within the next month. My time is of high demand these days with a 1yr old daughter!

Next up - I need to bring my brain back into my high school days and see if I can still remember how to weld!

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