How important are grounded outlets for old test equipment? - Page 1
Forum section: electronics / projects

author: ez24
author_rank: Super Contributor
timestamp: May 04, 2015, 10:56:58 pm
content: I saw this from another post:QuoteMy old house does not have grounds. How important is this with old analog equipment? I have a Wavetek 145 and a Hitachi analog scope and both seem funny. I just assumed they are both bad. I just cannot get any wave forms that make sense. I assumed the scope has no trigger, it is very tough to get a stable waveform. If I do get something, like a square wave, and come back in a few hours, it will always be gone. Since my equipment is floating (I cannot see it move) and floating implies movement and this implies instability, this seems to be what is happening.Is it possible my problems are related to the fact I do not have a ground? I sure hope I do not have to drive in ground rods and run wires in through the window, but I sure would like to get my stuff to work.thanks

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 04, 2015, 11:40:25 pm
content: Green-wire safety ground in the mains power cord is important for safety when using mains-powered electrical gear (including test equipment).However, the green-wire safety ground should have nothing to do with the stability and functionality of your test gear.Is your scope not even able to trigger on its own test signal? (assuming it has a test signal since you did not identify the model).it sounds more like the trigger circuit of the scope is broken vs. having anything to do with the mains safety-ground.Also assuming you are properly connecting the output of the function generator to the input of the scope.Since you included no details there, either, we are unable to offer any response.You also did not mention how you are connecting this gear to your mains power source.For example: if you were using a modern, grounded power strip to power the signal generator and scope, that would connect the green-wire power grounds together, even if the power strip itself were NOT grounded because of the deficiencies of your mains wiring.

author: ez24
author_rank: Super Contributor
timestamp: May 05, 2015, 06:55:35 am
content: QuoteNo - it is Hitachi V-1050, it has a test output, cannot sync on it, ie no stable signalQuotebummerSometimes I can get it to sync on a signal from the sig gen but it looks like a sweep function. For example one cycle will be on the left side and 5 cycles on the right.QuoteWith a BNC to BNC cable. If I play around with the controls a lot, sometimes I can get it to lock onto a square wave for awhileQuoteMy wall outlet is 2 prong. I have an 3 prong extension cord going to the desk. I had to break off the ground plug so it would plug into the wall. I have a 3 prong outlet box plugged into the extension cord and the equipment plugged into the power strip.Quotehuh? my 3 prong power strip is connected to my wall via a 2 prong plugI am sure now the scope is no good, I have 3 sources, 1. the built in 2. the Wavetek 145 3. a voltage ref with a square wavetime to dry off the tears and start saving for a new oneglad to know it is not my wires

author: Richard Head
author_rank: Frequent Contributor
timestamp: May 05, 2015, 09:04:33 am
content: My old house does not have grounds.I wonder what wiring code your house complies with?I find it scary that there is no earth lead at all. You obviously don't have an RCD in the panel also.So basically if you have a live wire accidently touch the metal chassis of an appliance nothing will trip out, allowing somebody to be electrocuted. Is this for real?I can see this being ok if all appliances are double insulated but you can't do that with big stuff like washing machines etc.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 05, 2015, 12:23:21 pm
content: Quote from: Richard Head on May 05, 2015, 09:04:33 amOh you kids! His "OLD" house complies with the electrical codes that were in placewhen it was built.Several generations of humans managed to survive between the general introduction of electricity and the advent of RCD, GFCI, etc. And even before safety grounds became a requirement. But you knew that.

author: Richard Head
author_rank: Frequent Contributor
timestamp: May 05, 2015, 12:28:12 pm
content: Sorry dad!

author: DanielS
author_rank: Frequent Contributor
timestamp: May 05, 2015, 12:40:48 pm
content: Quote from: Richard Head on May 05, 2015, 09:04:33 amOld constructions from 60+ years ago. Many electrical codes did not require ground back then. My mother's house did not have ground either until she had the house re-wired about 25 years ago due to pressure from insurers to replace her aluminum wiring.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 05, 2015, 12:41:47 pm
content: Quote from: ez24 link=to)pic=47322.msg666723#msg666723 date=1430808935Yes, as I said. But your 3-outlet extension cord connects together the green-wire safety grounds of the oscilloscope and the generator. Even if you broke of the ground pin of the extension cord plug (shame on you!)Note, that if you were really worried about safety, you could use a plug-in GFCI. Or retro-fit the wall plug with a protected version. GFCI does NOT require a connection to ground to operate properly. It operates on the principle of differential current. If the same current doesn't return on the neutral that went out on the hot wire, then the current must be going somewhere else, and THAT trips the breaker. No ground reference required.

author: ez24
author_rank: Super Contributor
timestamp: May 05, 2015, 04:59:07 pm
content: My house was built in 1911. I am not worried about the electricity, I worry about earthquakes. I live in So Calif. The house I live in was a Sears kit house (talk about kits !) and no thought was given to earthquakes then.QuoteI did not know 2 prong CGCI existed. Just a quick look on Amazon, I cannot find one. Since I live in the Nanny State, I am sure I will not find one at local stores, but I will keep looking, it would be a good idea to have one. thanks

author: DanielS
author_rank: Frequent Contributor
timestamp: May 05, 2015, 06:18:42 pm
content: Quote from: ez24 on May 05, 2015, 04:59:07 pmThe principle is quite simple: use a transformer with an equal number of turns from both live and neutral in it and unless there is leakage to somewhere else, the return current should be identical to the live current, canceling the net magnetic field. A third winding senses the net field and trips the breaker if a large enough imbalance appears.Three pins GFCIs work the same way, they simply pass ground through.

author: ciccio
author_rank: Frequent Contributor
timestamp: May 05, 2015, 08:30:34 pm
content: Quote from: Richard Head on May 05, 2015, 09:04:33 amHe can install an RCD even without ground, and it will operate (if needed).Part of my house (50 years old) does not have a ground conductor, but an RCD is installed ad it will (hopefully) protect from being electrocuted..RCDs don't need ground for proper operation.http://en.wikipedia.org/wiki/Residual-current_deviceOn the other side, if I touch both live and neutral I'll surely will be electrocuted, but even with a ground connection the RCD will not trip.Best regards

author: JBaughb
author_rank: Regular Contributor
timestamp: May 05, 2015, 09:22:50 pm
content: Quite common in parts of the US. Sometimes the ground line is available but the outlet doest support it. Might be possible to get a grounded outlet and swap that in (IF you are knowledgable) Shut off the breaker, and don't kill yourself.A friend had to swap out all the outlets in a house he purchased. It was just a weekend project and a few hundred bucks.