Kegconnection Complete Starter Kit and More Giveaway!


Home Brew Forums > Home Brewing Beer > Electric Brewing > 3 wire 240v GFCI question

Reply
 
LinkBack Thread Tools
Old 03-28-2011, 04:38 AM   #21
Wberry
Feedback Score: 0 reviews
Recipes 
 
Join Date: Mar 2011
Location: Huntington Beach, Ca
Posts: 68
Default

First, thelorax121 - sorry for half hijacking your thread here; but, this is a good topic of discussion for those interested in a bit of theory. Additionally, if there are any TV/Radio Station Electricians that want to chime in - Please Do! They have the bigger problems with grounding and isolation then you can possibly imagine!

Quote:
Originally Posted by samc View Post
How would he go about grounding a PID that does not have a ground? Not sure what OP is using but for example Auber PID that I have does not have a ground terminal and the case is plastic.
OK so on the theoretical level and this is probably WAY too deep for this discussion - and to that end I think I went a bit off the deep end with my previous post; but, for the interested here is the control theory...

When utilizing PID controllers without a case, line, or sensor ground, you want the thermocouple (your temp sensor) to be electrically isolated from your entire system. Isolated/Ungrounded thermocouples have a much slower response time but an increased safety and control factor. This isolated state allows the controller to set its own ground/zero potential plane where ever it so chooses - +5V, -5V, +20V, 8002V, does not matter.

When utilizing PID controllers WITH a case ground and non-isolated sensor is when things become a bit tricky. You might want the high response with a steam system which has the capability to rapidly heat fluids. Hypothetically ... suppose your SSR, pump, or other piece of equipment is leaking current via its case and has raised the ground plane from 0V to 5V - meaning that 5 volts of potential is leaked back to the ground line through your entire system and your total potential between Line and Ground is now 115VAC as opposed to 120VAC. In order for the controller to not to have skewed input data, its ground plane at the controller must additionally be raised by 5V, there by putting the sensor and PID controller at the same reference potential.

This is why you have to match the style of thermocouple to the style of controller and additionally shows the importance of proper grounding NOT JUST FOR CURRENT but additionally for equal references for your electronics.

Sorry for the tangent but hopefully someone will find some resolution to their problems here.

Peace
__________________

Drinking: American Amber, Kolsch-Style, American Blonde
Bottled: Falconers Flight IPA, Falconers Flight IPA w/Raspberries, AG BIAB Kolsch-Style
Primary: AG Kolsch-Style #2
On Deck: Bee Cave Haus Pale on Peaches


Last edited by Wberry; 03-28-2011 at 04:40 AM.
Wberry is offline
 
Reply With Quote Quick reply to this message
Old 03-29-2011, 01:44 AM   #22
rhoop
Feedback Score: 0 reviews
Recipes 
 
Join Date: Mar 2011
Location: Calgary, Alberta
Posts: 156
Liked 14 Times on 11 Posts

Default

Hmm. Very interesting! So your suggesting that a separate ground be run for the PID if possible, and if not, making sure the thermocouple is isolated? Makes sense! I still wonder what caused both GFCI's to trip? There must be some sort of potential difference somewhere in the ground/neutral system to cause it. If it was one or the other, that would be easy, but both at the same time...

__________________
rhoop is online now
 
Reply With Quote Quick reply to this message
Old 03-29-2011, 09:09 PM   #23
thelorax121
Feedback Score: 0 reviews
Recipes 
 
Join Date: Apr 2009
Location: Athens GA
Posts: 419
Liked 1 Times on 1 Posts
Likes Given: 1

Default

Yea I am still stumped about that as well, but as soon as I removed the g/n wire coming off the inlet from the gound bar and capped it, everything worked beautifully. As for grounding the PIDs, any idea on how to go about this, or how would you isolate the RTD sensors? Also, you metion that isolating may slow down the response time, by what degree do you think?

__________________
thelorax121 is offline
 
Reply With Quote Quick reply to this message
Old 03-29-2011, 11:07 PM   #24
P-J
HBT_LIFETIMESUPPORTER.png
Feedback Score: 0 reviews
Recipes 
 
Join Date: Mar 2010
Location: Charlotte, NC
Posts: 3,231
Liked 244 Times on 196 Posts
Likes Given: 430

Default

Quote:
Originally Posted by thelorax121 View Post
...
As for grounding the PIDs, any idea on how to go about this, or how would you isolate the RTD sensors? ...
The PIDs do not require grounding and have no provision for doing that either. As far as isolating the RTD goes, it is electrically isolated from the get go. The probe shell does not have any electrical connection with the sensor wiring. The probe wiring is isolated by the PID circuits - no worries.
__________________
P-J is offline
 
Reply With Quote Quick reply to this message
Old 03-30-2011, 12:28 AM   #25
Wberry
Feedback Score: 0 reviews
Recipes 
 
Join Date: Mar 2011
Location: Huntington Beach, Ca
Posts: 68
Default

Sorry for the late reply here ...

GFCIs are a tricky subject. I have (2) possible guesses:

First, your pump(s) are leaking a bit (something over 5ma) of current across their windings, which is dissipated through the path of least resistance ... your ground on the 240V connection. In this case you would develop an imbalance in the GFCI supplying the motors and you have a false trip.

Secondly, your heating element has been saturated with moisture and upon firing it up there is a significant leakage to ground. This would additionally provide an imbalance between the GFCI's lines causing a trip.

The NEC is relatively particular about the utilization of GFCIs where ever the chance for water and electricity could meet; but, your situation is slightly complex with the mixture of 120V & 240V needs. In this instance, I would think the code correct way to wire your system would be as follows:

Have a 50A 4 wire receptacle installed. Then run your horse c**k of an extension cord (LOL) to your rig with a hard-wired connection at your control box. In the rig's NEMA 12 enclosure, I would mount a 50A mains breaker that then branch feeds several VERY tight curve breakers. You could then utilize an in-line GFCIs to protect your receptacles for your equipment. OR, you could switch the windings on your motor and see if your electronics will take 220 and power it all off the same circuit.

The only reason why I bring this up is that technically you are feeding a single device from (2) power sources and there is no single way (breaker/cord/gfci/etc) to remove power from the rig. Enough on that topic and back to the PID stuff ...

The short version of what I posted earlier is that there are (in simple terms) (2) predominant styles of thermocouples - ones without a ground and ones with. You need to make sure that, which ever style thermocouple you use, it is paired correctly with the same style of controller. Ungrounded thermocouples are very easy to install and relatively noise immune - their downside is their slow response time. Very fast responding thermocouples are grounded and require a significant amount of design energy in searching for possible electrical interference that can alter the reference plane.

I would bet that your sensors are isolated and that any shielding they have for electrical interference is taken to case ground where they meet your HLT/MLT/Kettle. Sorry, If I took you off track looking for other possible issues that likely do not exist.

Peace

__________________

Drinking: American Amber, Kolsch-Style, American Blonde
Bottled: Falconers Flight IPA, Falconers Flight IPA w/Raspberries, AG BIAB Kolsch-Style
Primary: AG Kolsch-Style #2
On Deck: Bee Cave Haus Pale on Peaches

Wberry is offline
 
Reply With Quote Quick reply to this message
Old 03-30-2011, 02:31 AM   #26
rhoop
Feedback Score: 0 reviews
Recipes 
 
Join Date: Mar 2011
Location: Calgary, Alberta
Posts: 156
Liked 14 Times on 11 Posts

Default

The motors could easily trip it, and the moisture in the element, but it would be a pretty big coincidence if it happened at the same time! Or does the controller do the pumps through control contacts not on the diagram as well as control the heat element? Are both GFCI's inline? Maybe they monitor ground as well as the common. Then it would be something as simple as some ground current, which we've already established. Do the GFCI's in the states monitor ground? I don't know of any consumer grade ones that do here in Canada, but then again, electricity works completely different once you cross the border.

__________________
rhoop is online now
 
Reply With Quote Quick reply to this message
Reply


Quick Reply
Message:
Options
Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Type of wire for 5500w 240v element thomashp Electric Brewing 14 03-04-2011 10:35 PM
2 Pole GFCI Breaker With 4 Wire Cord? ScubaSteve Electric Brewing 8 02-08-2011 06:37 PM
240V Extension cord question for the gurus jflimbo Electric Brewing 3 01-18-2011 10:24 PM
Strange issue with 240v legs. 120v on both, no 240v Brewmoor Electric Brewing 5 12-03-2010 06:15 PM
Multiple GFCI wiring question Cpt_Kirks Electric Brewing 8 10-20-2010 03:22 PM