Hi soongsc,
That would seem to be a diabolical thing to do to someone! Continuity tests would show a ground is present, but a spike of current would behave as if there was little to no safety ground connection.
I wouldn't even joke about doing this.
-Chris
That would seem to be a diabolical thing to do to someone! Continuity tests would show a ground is present, but a spike of current would behave as if there was little to no safety ground connection.
I wouldn't even joke about doing this.
-Chris
Hi soogsc,
I guess it really depends on how much inductance there is, but there are now two extra connections in series in the ground path.
No way am I a fan of this.
I guess it really depends on how much inductance there is, but there are now two extra connections in series in the ground path.
No way am I a fan of this.
ground (earth) is separately derived
Health care often uses isolated power, most often isolation transformers. Critical research labs sometimes use generator driven isolated power. Also always the ground (earth) is also separately derived. The reason for all this is not just to protect against arc flash and arc blast kind of stuff but to protect against stray current through a patient. Sometimes the designers will say that the isolated power is to protect the Operating Room or Heart Catheterization Lab from noise and distortion on the utility power. I see it the other way around, the power isolation is to protect the utility power from the lab.
One facility I traveled to had an odd event every day at 7:00am. Critical patient care equipment would trip offline. 7:00am was the time the local utility would switch in the Power Factor correction capacitors.
DT
Health care often uses isolated power, most often isolation transformers. Critical research labs sometimes use generator driven isolated power. Also always the ground (earth) is also separately derived. The reason for all this is not just to protect against arc flash and arc blast kind of stuff but to protect against stray current through a patient. Sometimes the designers will say that the isolated power is to protect the Operating Room or Heart Catheterization Lab from noise and distortion on the utility power. I see it the other way around, the power isolation is to protect the utility power from the lab.
One facility I traveled to had an odd event every day at 7:00am. Critical patient care equipment would trip offline. 7:00am was the time the local utility would switch in the Power Factor correction capacitors.
DT
Possible but you still dont have galv. isolation between the analyzer and the generator section.
The AP system One also had isolation transformers at the generator outputs to achieve isolation. But they also had a post-amplifer with isolated supply if I remember correctly.
hi guys, the topic becomes a sort of lessons learnt or Faq on RTX and this may not be bad.
thx mbrenna for your wiki page. good idea and goo stuff so far,
can anyone help me understand the following 2 ffts which I made this moning on a dual mono UCD400 with dual smps400A400.
I m concerned with the second FFT where we can see that the fft noise floor is gently going down from -100db to -145 but the other channel is quite flat around -130 -140db
how to interpret this fft decrease , which is also masking the bins value?
another question is about 50hz (and harmonics peak): in some other tests with an amp on the bench accepting true différential input I never get these 50hz stuff.
FYI the UCDs were connected with their 3 wires (0v + -) to the RTX XLR 1 2 3 and on the amp the 0V is not connected to the gnd box (its dual mono and I didnt couple their 0V on the box or on anything)
the signal was 2.5V into 6 ohms and measure with input at 3.16V
thanks
thx mbrenna for your wiki page. good idea and goo stuff so far,
can anyone help me understand the following 2 ffts which I made this moning on a dual mono UCD400 with dual smps400A400.
I m concerned with the second FFT where we can see that the fft noise floor is gently going down from -100db to -145 but the other channel is quite flat around -130 -140db
how to interpret this fft decrease , which is also masking the bins value?
another question is about 50hz (and harmonics peak): in some other tests with an amp on the bench accepting true différential input I never get these 50hz stuff.
FYI the UCDs were connected with their 3 wires (0v + -) to the RTX XLR 1 2 3 and on the amp the 0V is not connected to the gnd box (its dual mono and I didnt couple their 0V on the box or on anything)
the signal was 2.5V into 6 ohms and measure with input at 3.16V
thanks
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Last edited:
Problem with REW. The peaks are quite similar, restart the measurement again by clearing the average, and it should go down.
Actually even in the NEC a GFCI can substitute for a safety ground. Its actually better since it trips at 10 mA not 20A like the main breaker. However the ground loop issues are not there.
Best way to understand the issue is to draw it out including the leakage currents through the various power transformers etc. and the the voltage differences across the grounds. it gets complex quickly and will illustrate why its not easy to predict or deal with.
If the RTX input is used differentially and the common mode it in range then the only issue is the difference between the RTX chassis and the DUT chassis. First step, measure the voltage difference with both operating and not connected to each other. It should be less than 3V. If its higher stop and figure out why. (Common problem is an input line filter with caps to the chassis and the chassis not connected to safety ground) Then measure the AC current between the chassis when shorted through the meter. If there is any to speak of stop and figure out why. Sometimes all you need is a substantial (12 AWG or so) wire between the chassis. Use the ground jack on the front of the RTX so you don't go through the audio circuits (hopefully).
Hey Demian,
So similar but different....I picked up another HTPS 7000, but this one is the
first version, the one we have the schematic for... it came to me w/o the ground
safety pin...(broken off or removed).
I recall some similar statement but in that instance, I should'nt use it until that plug
has been cut off and new one installed.
new end installed with the ground pin intact. Will it work through a GFCI
receptacle?
Cheers,
So similar but different....I picked up another HTPS 7000, but this one is the
first version, the one we have the schematic for... it came to me w/o the ground
safety pin...(broken off or removed).
I recall some similar statement but in that instance, I should'nt use it until that plug
has been cut off and new one installed.
new end installed with the ground pin intact. Will it work through a GFCI
receptacle?
Cheers,
You can put a hardware store style three wire plug on the wire, and curse the idiot that snapped the pin off.
-Chris
-Chris
Hi Demian,
Well, the GFI works with a three wire system. It'll remove power right away as you've pointed out. Still, the safety ground should always remain intact if the equipment was designed for it.
I've got an nice old HP 6236 power supply where someone broke off the ground pin. There isn't even any reason to do that as the supply is floating wrt ground.
You made a good point about the ground differential and it not being too far off from the two units. If it is you have serious issues that need addressing before measurements are attempted.
-Chris
Well, the GFI works with a three wire system. It'll remove power right away as you've pointed out. Still, the safety ground should always remain intact if the equipment was designed for it.
I've got an nice old HP 6236 power supply where someone broke off the ground pin. There isn't even any reason to do that as the supply is floating wrt ground.
You made a good point about the ground differential and it not being too far off from the two units. If it is you have serious issues that need addressing before measurements are attempted.
-Chris
Hi soogsc,
Just because people sell a product for an application, that doesn't make it right or safe. I think those are intended to be installed into equipment at the point of manufacture.
-Chris
Just because people sell a product for an application, that doesn't make it right or safe. I think those are intended to be installed into equipment at the point of manufacture.
-Chris
RE Monster HTS7000
The isolated outputs have GFCI's. It has a switch for isolated or balanced power at each transformer isolated output. Turn off the display. it radiates. it was necessary to sell the box. I got push back over mechanical meters.
The isolated outputs have GFCI's. It has a switch for isolated or balanced power at each transformer isolated output. Turn off the display. it radiates. it was necessary to sell the box. I got push back over mechanical meters.
This is a complete a misunderstanding and or a misrepresentation.
The NEC National Electric code is written by the NFPA National Fire Prevention Association, The NFPA name for the document is NFPA 70.
NFPA 70: National Electrical Code(R)
NFPA 70 is a fire life safety code, not every code requirement is shock safety related. No single requirement or exception is better than the other. Perhaps no one wants the building to burst into fire and burn down. For example, GfI’s are required to protect 20 amp lighting circuits and have nothing to do with shock protection. The purpose of the GFI is to protect the upstream transformer.
A green or bare grounding conductor is required for every 15 and 20 amp receptacle, the exception is existing buildings. There is no retroactive requirement.
Additionally GFCI’s are required in kitchens bathrooms, boathouses, laundry, garage and outdoor locations within 6 feet of the ground. The ground being that cold damp concrete that you stand on in your bare feet. If you can reach or stand on ground a GFCI is required
How about that? We have code requirements for both the green or bare grounding conductor and a GFCI. Now we have the exception. For existing buildings we have only a hot wire and a neutral wire, there is no grounding conductor there is no provision to plug in a 3 prong cord cap. Some of us would cut off the ground and plug it in. No No never cut off the ground. The code exception allows the installation of a GFCI to accommodate the grounded cord cap. The reasoning is that some level of protection is better than none.
Strange to me, almost exclusive to the NEC the exception is the rule, sort of.
In terms of safety, I do not have a Moderator’s feigner to wag. I will do it anyway.
DT
Last edited:
I have never heard of a Ground Fault Circuit Interrupter's function as protecting upstream transformers. The traditional ground wire function was to be a low resistance return path that will ensure that the circuit protection will open if line power comes in contact. That's the reason the gauge of the ground return was increased (in the 1970's I think) to ensure that it would handle the fault current and ensure that the fuse or breaker will open.
GFCI's trigger on unbalanced current passing through them. Its an indication of a leakage path and it doesn't need to be a lot, just 10 mA that came from one side (LorN) and did not return on the other.
Here is a primer from NEMA: https://www.nema.org/Products/Documents/NEMA-GFCI-2012-Field-Representative-Presentation.pdf
Here is a history of NEC required applications. I don't see anything about 6 feet from "ground". 6 feet from a wet location which has since been revised. However every community has the option to vary from the NEC depending on local issues.
DATES GFCI REQUIREMENTS WERE ESTABLISHED:
1971 Receptacles within 15 feet of pool walls
1971 All equipment used with storable swimming pools
1973 All outdoor receptacles
1974 Construction Sites
1975 Bathrooms, 120-volt pool lights, and fountain equipment
1978 Garages, spas, and hydromassage tubs
1978 Outdoor receptacles above 6ft.6in. grade access exempted
1984 Replacement of non-grounding receptacles with no grounding conductor allowed
1984 Pool cover motors
1984 Distance of GFCI protection extended to 20 feet from pool walls
1987 Unfinished basements
1987 Kitchen countertop receptacles within 6 feet of sink
1987 Boathouses
1990 Crawlspaces (with exception for sump pumps or other dedicated equip.)
1993 Wet bar countertops within 6 feet of sink
1993 Any receptacle replaced in an area presently requiring GFCI
1996 All kitchen counters – not just those within 6 feet of sink
1996 All exterior receptacles except dedicated de-icing tape receptacle
1996 Unfinished accessory buildings at or below grade
1999 Exemption for dedicated equipment in crawlspace removed
We should get back to the audio analyzer. This is getting a little off track.
GFCI's trigger on unbalanced current passing through them. Its an indication of a leakage path and it doesn't need to be a lot, just 10 mA that came from one side (LorN) and did not return on the other.
Here is a primer from NEMA: https://www.nema.org/Products/Documents/NEMA-GFCI-2012-Field-Representative-Presentation.pdf
Here is a history of NEC required applications. I don't see anything about 6 feet from "ground". 6 feet from a wet location which has since been revised. However every community has the option to vary from the NEC depending on local issues.
DATES GFCI REQUIREMENTS WERE ESTABLISHED:
1971 Receptacles within 15 feet of pool walls
1971 All equipment used with storable swimming pools
1973 All outdoor receptacles
1974 Construction Sites
1975 Bathrooms, 120-volt pool lights, and fountain equipment
1978 Garages, spas, and hydromassage tubs
1978 Outdoor receptacles above 6ft.6in. grade access exempted
1984 Replacement of non-grounding receptacles with no grounding conductor allowed
1984 Pool cover motors
1984 Distance of GFCI protection extended to 20 feet from pool walls
1987 Unfinished basements
1987 Kitchen countertop receptacles within 6 feet of sink
1987 Boathouses
1990 Crawlspaces (with exception for sump pumps or other dedicated equip.)
1993 Wet bar countertops within 6 feet of sink
1993 Any receptacle replaced in an area presently requiring GFCI
1996 All kitchen counters – not just those within 6 feet of sink
1996 All exterior receptacles except dedicated de-icing tape receptacle
1996 Unfinished accessory buildings at or below grade
1999 Exemption for dedicated equipment in crawlspace removed
We should get back to the audio analyzer. This is getting a little off track.
Hi Chris, Thanks I've got one to put on it. 🙂
Hi Demian, okay will do, I didn't know that about the display.
Is the display radiation the same for both HTS7000 and the HTPS7000 MKII or
only the HTS7000?
The good folks I got the HTS7000 from must have left the back side down
then it must have suffered from a flood. or left outside, something.
All the gold connectors in the back are all corroded flaking and turning green.
I think the outlets are fine and firm. Burried in the queue to be looked at
when the bench/shelves are finished and all installed. Oh the joy.
Yes on topic...so much for tossing a hair driver in the tub in modern
homes with GFCI.
Pardon me Inspector, whadda mean it was plugged in through a 14 gauge
extension cord that was plugged into the bench supply?
The audio analyzer said THD was really good, THD + N, well maybe
that IS what I heard. I'll have to check the FFT results, won't be ready for days.
Cheers,
Hi Demian, okay will do, I didn't know that about the display.
Is the display radiation the same for both HTS7000 and the HTPS7000 MKII or
only the HTS7000?
The good folks I got the HTS7000 from must have left the back side down
then it must have suffered from a flood. or left outside, something.
All the gold connectors in the back are all corroded flaking and turning green.
I think the outlets are fine and firm. Burried in the queue to be looked at
when the bench/shelves are finished and all installed. Oh the joy.
Yes on topic...so much for tossing a hair driver in the tub in modern
homes with GFCI.
Pardon me Inspector, whadda mean it was plugged in through a 14 gauge
extension cord that was plugged into the bench supply?
The audio analyzer said THD was really good, THD + N, well maybe
that IS what I heard. I'll have to check the FFT results, won't be ready for days.
Cheers,
Last edited:
We are mostly in agreement other than me bristling about GFCI’s being better than grounded receptacles, except the limited exceptions they are both code requirements.
I could tell from the conversation there is confusion regarding the difference if any between GFI’s and GFCI’s.
Dig into the NEC. GFI's and GFCI's are different creatures.
GFI's came about to protect the step down transformers for comertial lighting. Single 20 amp circuits were taking out entire systems. The GFI came about to correct that. They trip at 20 amps not 20 ma. You do not want a lighting circuit taking out the power to your frozen embryos.
6’- 6” above grade is pretty much 6 feet above the cold damp concrete slab in your garage. At least that is the visual I use when I teach it. The next power point is a person being the path to ground; you know your bare feet on that cold damp concrete.
Why do I call the concrete ground?
Ufer ground - Wikipedia
Okay I am done, back to bin size and noise floor
DT
Long time California Hospital Inspector, Engineering Consultant
I could tell from the conversation there is confusion regarding the difference if any between GFI’s and GFCI’s.
Dig into the NEC. GFI's and GFCI's are different creatures.
GFI's came about to protect the step down transformers for comertial lighting. Single 20 amp circuits were taking out entire systems. The GFI came about to correct that. They trip at 20 amps not 20 ma. You do not want a lighting circuit taking out the power to your frozen embryos.
6’- 6” above grade is pretty much 6 feet above the cold damp concrete slab in your garage. At least that is the visual I use when I teach it. The next power point is a person being the path to ground; you know your bare feet on that cold damp concrete.
Why do I call the concrete ground?
Ufer ground - Wikipedia
Okay I am done, back to bin size and noise floor
DT
Long time California Hospital Inspector, Engineering Consultant
Last edited:
DC on the signal, or very low frequency noise? That might produce some leakage to higher frequencies and skew the FFT base line. Make sure the DC filter is switched on at the RTX ("AC" LED is on). You could try swapping the wires between the channels to figure out where the difference between the two channels is happening.
Ground faults on 20A circuits were taking out entire systems because the main breaker upstream had code-required GF protection, and the little 20A branch breaker did not. So with a ground fault, the main breaker's GF protection was faster than the 20A overcurrent device, and the main breaker tripped. They add a second level of GF protection simply to coordinate with upstream protection.
Secondary GF protection in any form has nothing to do with protecting the upstream transformer. It is there to reduce fires on the equipment that has faulted, as ground faults are normally arcing faults. Transformers could care less if they have a secondary ground fault, to the transformer it's no different from other types of through faults. We won't get into the 58% issue.
GFCI is all about personnel safety, in the mA range. System GF protection is about fire avoidance, in the 1A - 1200A range. The fire risk is at the faulted equipment, not the transformer.
Long time PE in 5 states, including California.