my profile | my password | search | faq & rules | forum home

» Film-Tech Forum ARCHIVE   » Community   » Film-Yak   » Electrical Safety question

Author Topic: Electrical Safety question Richard Hamilton Phenomenal Film Handler Posts: 1341 From: Evansville, Indiana Registered: Jan 2000 posted 06-02-2008 09:08 AM                     This weekend my parents air conditioning in their house quit. I looked at it Saturday morning and found that it had a bad transformer which feeds the control circuit. The bad transformer had a Line input of 240VAC with the load being 24VAC. I could not find a replacement transformer with an input of 240VAC. What I bought was a transformer with an input of 120VAC. My question/concern is this: The air conditioning unit has 220V and a ground coming into it. I hooked the new transformer up with one side of the input to one leg of the 220V and the other side going to ground (since there is no neutral). Are there any safety issues because I am using a ground instead of neutral? I don't want to go outside and lean against the AC unit and end up looking like Yahoo Serious! Thanks, Rick  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 06-02-2008 09:15 AM                     Not really. The secondary is obviously isolated fomr the primary and as asuch the control circuitry wouldn't be in danger. I suggest however that you get the correct tranny fomr the manufacturer or at least one at Grainger as the ooriginol may have been thermally protected in such a way as to prevent a fire. Mark.  |  IP: Logged Richard Hamilton Phenomenal Film Handler Posts: 1341 From: Evansville, Indiana Registered: Jan 2000 posted 06-02-2008 09:38 AM                     thanks Mark, I will tell the AC company to bring that part before they come to do their PM call on it soon. I was just concerned about the safety of the electrical. It was one of those " I can make it work, but its not right" fixes, and I wasn't sure about the electrical. And I didn't want to call a service company on the weekend to replace a $17 part. Rick  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 06-02-2008 12:37 PM                     I agree! ou may want to just get the part yourself and save some on that too. The HVAC company will probably double or triple their cost on it to you.... Mark  |  IP: Logged Bruce Hansen Jedi Master Film Handler Posts: 847 From: Stone Mountain, GA, USA Registered: Dec 1999 posted 06-02-2008 05:28 PM                     There should not be current flow on a ground line. Any time there is current flow on a wire, there will be a voltage drop on that wire (E=I*R). Your A/C casing would have a voltage on it. Now here is reality: the current that xformer is going to draw is fairly low, and therefore the voltage drop would also be very low. This should work until you can get the correct part.  |  IP: Logged Charles Greenlee Jedi Master Film Handler Posts: 801 From: Savannah, Ga, U.S. Registered: Jun 2006 posted 06-02-2008 05:33 PM                        quote: Bruce Hansen E=I*R Reminds me of high school physics every time I see Ohm's law. Or teacher sang it to the tune of "Twinkle Twinkle little star" It was sooo stupid, I actually remember it. "Twinkle Twinkle little star, E equals I times R."  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 06-02-2008 06:32 PM                        Most popcorn machines and stoves are wired "that way." The neutral is also the ground. New rules require 4 wire (2 hot, ground, and neutral)but there are PLENTY (including my house) that are wired the old, 3 wire way. Works out OK as long as the ground/neutral is oversized. Louis  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 06-02-2008 08:00 PM                     Ground and Neutral are certainly not the same and what you did is certainly not safe and not to code. While Neutral and Ground do go to the same place (Earth), what Bruce stated is absolutely correct. There is no way to conduct electricity without causing a potential difference and thus raise the "ground" to a potential above ground. It compromises the entire grounding of the building and the safety of the wiring as the ground is not allowed to have a potential. The code has traditionally been...the first load-center (breaker panel) after a step down transformer may connect the Neutral and Ground busses together as they are one and the same at that point and ONLY that point. This is because that is where the building's ground rod is tied to the panel...the potential at the busses will be identical. Any sub-panels after that, including any branch circuits MUST have a separate ground. Since there will be current flow on the Neutral (unless the currents are prefectly balanced), the Neutral and ground will be at different potentals all all circuits. Can you get away with it electrically in a pinch.....sure, you did...is it safe...not really, depending on the wiring. Steve  |  IP: Logged Richard Hamilton Phenomenal Film Handler Posts: 1341 From: Evansville, Indiana Registered: Jan 2000 posted 06-02-2008 08:36 PM                     Thanks for the replies. I was curious about the safety issue, it will be replaced this week. I was just in a "pinch" and wanted my parents to have air conditioning this last weekend. The ground wire/neutral that I hooked up from the transformer is physically screwed into the sheet metal of the AC unit, the 120AC line I'm getting is from one side of the contactor. The old transformer got the 220VAC from the input to the contactor.  |  IP: Logged Stephen Furley Film God Posts: 3059 From: Coulsdon, Croydon, England Registered: May 2002 posted 06-03-2008 02:00 AM                     Richard, You said: quote: Richard Hamilton I hooked the new transformer up with one side of the input to one leg of the 220V and the other side going to ground (since there is no neutral). Where is this? Your location is given as China, but getting 120 ish Volts by connecting between one leg and ground sounds like the US or Canada, with a centre tapped supply, yet you also mention 220V, which isn't a standard Voltage there. There are major differences between electrical systems, and regulations in different places. I can't see any way that you could connect a 120V transformer in this way in China.  |  IP: Logged Richard Hamilton Phenomenal Film Handler Posts: 1341 From: Evansville, Indiana Registered: Jan 2000 posted 06-03-2008 06:01 AM                     Stephen, sorry about that! I am staying at my parents in the States now, will be back in China probably next month. Rick  |  IP: Logged Fred Tucker Film Handler Posts: 90 From: Sugar Land, TX Registered: Sep 2007 posted 06-10-2008 03:47 AM                     THe reason you didnt have a neutral on old stoves, dryers and the like is there were no electronics or accessories that required 120V. With the advent of such things as LED clocks on the stove, the code changed to allow for this safely. Was twsisting wires long before I fell in love with film.  |  IP: Logged Stephen Furley Film God Posts: 3059 From: Coulsdon, Croydon, England Registered: May 2002 posted 06-10-2008 12:50 PM                     quote: Fred Tucker the code changed to allow for this safely. I doubt that there's actually any safety issue here, though it may be required by regulations which claim to be on grounds of safety. In the roughly half of he world which has a single phase Voltage of around 240V dryers, cooks etc have lamps, moters, electro-mechanical timers etc. operating on 240V without large numbers of people being killed by them. At one time there was probably an issue of being able to use standard, readily available, parts, but these days the same factory, probably in China, is likely to be making components for use in many different countries, with different Voltages. Also, these days things like timers are likely to be electronic devices operating on a few Volts d.c., and this could be derived just as well from 240V as from 120V, so there's probably no great advantage in having a neutral available these days. There is an advantage to 120V for small incandescent lamps are concerned, and 120V ones are certainly more readily available in the US than 240V ones, but I doubt that it's really a safety issue. You could always use a 12V halogen lamp.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 06-10-2008 02:52 PM                        In fact, USA stoves have had 120v devices since at least the 1950's. The fluorescent light, oven light, and clock motor on my Mom's old 1959 stove are all 120v. The distinction is that the ground and the neutral cannot be the same now. Back then, they were the same wire....and no one died because the wire was large enough to hold, blowing the fuse in the "hot" wire. Conversely, the load return for 120v is now carried by the neutral; the ground is purely safety being tied from the frame to earth. Louis  |  IP: Logged

All times are Central (GMT -6:00)

Printer-friendly view of this topic

Hop To: Select a Forum: Category: Operations -------------------- Digital Cinema Forum Film Handlers' Forum Large Format Forum Ground Level Feature Info, Trailer Attachments & REAL Credit Offsets Category: Community -------------------- Film-Yak Film Handlers' Movie Reviews The Afterlife Bob Maar's Joke-A-Thon Category: Classified -------------------- Equipment and Supplies Wanted/For Sale Help Wanted/Seeking Employment Category: System -------------------- Software Beta Testing Forum

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.