How many volts?

Post new topic   Reply to topic

View previous topic View next topic Go down

Re: How many volts?

Post by Admin on Sat Jan 07, 2017 6:10 pm

Hi Densel,
Absolutely no problems.
As you say, the voltage level is "-48V nominal" which means that the actual figure may be somewhat higher. I think that this could be a grey area and subject to interpretation, depending on where you work.

Yes, at least in Europe one needs certification to handle high voltages. After seeing installations in Thailand I sometimes wonder if the installers have been certified (or if they need to be certified (English joke)). I am not too sure of the exact regulation but I also believe that high current also need certification. When I had my training it included "High Power". I also worked on up to 32,000 Volts.

810 A/h cells? Thats a lot of potential current. It will certainly make a mess of the odd spanner or wedding ring, if you are not careful.

> Sorry for these dumb questions.

Absolutely no problems at all. You are always welcome.

> ... but i didnt want to end up in your fasq pages.


Absolutely no fear of that. I have not added anything to the FASQ pages for years, and I do not intend to do so, so please do not fear that. Anything to share knowledge is good.


Very best regards from Harry


(PS - I see you have asked another question, but I will answer that later on - I returned to Sweden three days ago and I have to give Maj-Lis some attention)

_________________
(I will listen to 14.190MHz USB every Sunday afternoon 15:00 to 18:00 to mid July)
avatar
Admin
Admin

Posts : 365
Join date : 2012-11-24
Age : 65
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

Re: How many volts?

Post by Densil on Sat Jan 07, 2017 10:03 am

hej harry.

Thanks for your detailed reply. I was gonna ask you that question but i didnt want to end up in your fasq pages. so i guess that is an international or official voltage level for when you need to have certification? more than 50vdc or 35vac?

What about telephone exchanges and comms gear that uses -48vdc? -48vdc is a "nominal" value but it often comes from banks of leadacid batteries and 4x 13.8 is over 55vdc.

Where i work we have banks of 810 ampere 2v cells. 24 cells serial connected to get -48v. The real voltage is about 56v (measured).

Sorry for these dumb questions.
/D

Densil

Posts : 15
Join date : 2017-01-06

View user profile

Back to top Go down

Re: How many volts?

Post by Admin on Fri Jan 06, 2017 4:52 pm

Hello Densil,
Yes, I did indeed reply to the guy, and I did it politely. The question was badly phrased, I presume he meant "What voltage level is dangerous to humans?", and I gave him a serious reply.

If you are interested in the subject, then let me tell you a little story:

In 1968 I began my career as an "Electrophysiological Technician". My job was to put electrodes on peoples heads and chests and measure electrocardiographs, electroencephalographs and echoencephalographs. The problem with electrodes is that dissimilar metals create a voltage, so we used silver electrodes that were prepared by electrolysis to deposit silver chloride on them. There were also cloth pads to prevent light exposing the silver chloride, and the pads were wet with salt. In this way we could get the minimum resistance contact with skin.

These electrodes were placed directly on people heads and signals as low a 30uV were recorded.

When measured, the absolute lowest electrical resistance between two electrodes was about 5,000 Ohms. It made little difference if the electrodes were 1cm or 10cm apart; it was always about 5,000 Ohms.

In order to hurt someone you need to pass a current, and 1mA is a severe repremand, whereas 10mA is sufficient current to stop the human heart.

If you use Ohm's law (E = I x R) then you will see that the magical figure is 50 Volts. In fact, this is the internationally recognised level of a dangerous voltage; 50V DC. AC is a little different, since 35V AC (sinusoidal) has a peak voltage of 50V.

The answer to the original question "What voltage level is dangerous to human life?" is 50VDC or 35VAC.

Did you want to know this, or were you asking about the response I gave in my FASQ?

Very best regards, and welcome to the messageboard. Please feel free to ask questions. All sensible questions are answered. The others and SPAM are simply deleted.

Harry - SM0VPO (also EA/SM0VPO)

_________________
(I will listen to 14.190MHz USB every Sunday afternoon 15:00 to 18:00 to mid July)
avatar
Admin
Admin

Posts : 365
Join date : 2012-11-24
Age : 65
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

How many volts?

Post by Densil on Fri Jan 06, 2017 4:29 pm

hi harry - I saw that you had a fasq about how many volts it takes to kill someone. I saw your fasq post but what did you reply to the person who asked you the question. Did you bother to reply to him.
/D

Densil

Posts : 15
Join date : 2017-01-06

View user profile

Back to top Go down

Re: How many volts?

Post by Sponsored content


Sponsored content


Back to top Go down

View previous topic View next topic Back to top

- Similar topics

Post new topic   Reply to topic
 
Permissions in this forum:
You can reply to topics in this forum