I am very glad to have such a man whose knowledge, experience and expertise guide us in every field of electricity. Your great work will be fruitful for generations. Thank you sir
I think the most important conceptual point here is that the marginal increase in resistance of the electrode (rod) under test decreases as distance from the rod goes up. This means that as you go further away, eventually the resistance of the rod reaches a maximum value and will not increase thereafter. This is because the increase in resistance owing to distance is more than made up for the decrease in resistanace due to an increase in current path surface area. So the resistance between 2 rods at 30m could be the same value as the same rods 300 miles apart (asumming the same ground conditions).
Thanks for the practical video on earth rod testing as well referencing books, guidance. Sugestion: can you revisit the same place in summer next year and test the rod to test with dry soil?
Great video John, only had to do this once myself. I have a video idea, I recently had to setup a last man out switch for a large commercial property, switching several lighting circuits. This is something you could setup in your lab and maybe useful to others.
Strange request as it's bespoke circuitry and any customer wanting similar may have different requirements - it's not a 'one size fits all' type wiring.
@@Pengo4man What he sets up may not match what the customer wants. So much is done by copycat. That's why in the central heating world we have S plans and Y plans. So people can copy others' mistakes.
I've only seen the earth electrode test done once back in the late 90s for a remote located 2 x double stacked porta kabin office with lightning protection fitted and earthed at all 4 corners for an air control tower for Raf helicopter pilot training.
Hello, at minute 17.00 I didn`t quite understand how that method succeed in measuring only the Resistance of the electrode under test. The current is also flowing through R1, R2 and R3 in order to complete the circuit.
Hi John. Great video. Could I request a topic for your next one? I recently hooked up an old caravan (that was working perfectly when connected at home) to a powered site and found that every time I tried to use any load it tripped the RCD in the supply box. After checking the fuse board I found an earth-Neutral connection in the caravan. This makes sense, some current is returning from the load via the earth wire and bypassing the RCD in the supply box. My question is, what is the purpose of the earth-neutral connection and how is a caravan wired so it can be connected to either an RCD or no RCD protected supply?
I am wondering, is that low enough for a UK installation? Here in Belgium it MUST be under 100 Ohms, but you'll still need lots of RCDs to have a compliant system (whole house, bathroom, lights, one per 16 sockets, ... etc). It is advised to be under 30 Ohms, which most installations are. In that case you are only required to have 2 RCDs, one 300mA for the whole house and another 30mA for bathroom and some appliances (water heater, washing machine & dryer). I am not 100% sure but I think there are case where you may have more than 100 Ohms here, but it would require some annoying things like a 30mA hole house RCD ... etc
Almost all RCDs for UK homes are 30mA, and virtually all circuits have them. Theoretical maximum with a 30mA RCD is 1667 ohms, but generally under 200 is considered acceptable. Some older TT installations have a 100mA RCD, maximum for that is 500 ohms.
Very useful video. I have never seen this test and measurement done myself, so it is cool to see it. I have a question. Why the resistance doesn't change when you move the potential probe stake? What is theory behind this measurements. I guess it has something to do with the Ohm/squares.
Years ago a relative of mine had a conservatory build over their earth rod. A live-earth fault occurred (a foot of their fridge had crushed the cable) and the exposed metal of all their appliances was live.
Yes, even with a 50 ohms rod, current would be 230/50 = 4.6amps. However the wire will need mechanical protection at that size, such as steel conduit. Other minimum sizes in Table 54.1 in BS7671.
Yes, pretty standard Fall of Potential (FoP) test as you would hope a lightning protection specialist would do, however too often these days they carry out a 'dead earth' test using the the LPS as a reference electrode, which is not as accurate.
John, Kevin from across the pond. Ground rods are poor electrodes. Here in US if a rod is your only choice it must be 25 ohms or less for a single rod per NEC. If not add a second rod and you are done. I have a question, at 0:55 you said that if the earth ground rod was not connected to the consumer unit it would be dangerous. Do you not connect to other electrodes normally? And another question, what is the perceived danger if there is not an earth ground? Respectfully, Kevin
R. D. Your explanation is what about 99% of people think, but is not exactly correct. The purpose for Earth connections is for lightning, surges, and a 0 voltage reference point. It has pretty much no affect on the part of the system you describe. If live shorts to earth at an appliance in a residence, the electrical path is back to the consumer unit, to neutral, out to the utility transformer, through the transformer, back to the consumer unit, to the breaker and trips it. Thousands of amps. Very few amps go to the earth rod, which already happens before the short circuit existed. Electricity flows only in closed circuits and proportioned across all paths by the resistance. Respectfully, Kevin
R. D. Also, in US residential we have single phase that is 240 volts with a center tap neutral that is grounded. So 120 volts to ground. The 180 degrees is only because of the way an Oscope works. If you disagree with anything, m willing to discuss. Respectfully, Kevin
UK consumer units do not have any connection between neutral and earth. With a TT system, the electrode is the only earth connection. Other types of installation (TN-S and TN-C-S) have an earth connection provided from the electrical supply, and although it's possible to install your own supplementary earth electrode as well, that is rarely done as it's not required and wouldn't achieve very much even if it was.
@@jwflame thanks JW, a so called "engineer" told me to link N to E bus bar as living in Thailand use a TT system or a PME?, I didnt as it sounded very ODD
I am from India where TT earthing system is followed. Reason for not linking n and e: Imagine the service has floating neutral fault. The consumer doesn't notice this as the return path is now 100 per cent via linked earth. OK fine. One bad day the earth lead got snapped (may be due to corroded joint or mechanical damage). Now what will happen? As both return paths are open, all metallic parts (switch boxes, conduit pipes, appliance bodies etc) of the service will get energized thru the earth terminals. The appliances will not work as there is no return path. In this condition if you touch the metal parts, you become the return path and get electrocuted. Bonus point: RCCB is must for TT earthing system in order to protect us from leakage currents. Mcb or fuse is not intended to protect us. These work during long duration over loads and shorts for fire protection of wiring and property.
@@jwflame I disagree. I fairly disagree wrt insulation testing BUT it is valid for that. For conduction testing a normal MM should be fine. The important bits are the test electrodes inserted into the ground.
I wonder if you could look into the old WW1 trench telephones using earth current signalling? Bayonets spiked into the ground and field telephones. I can understand RF, but I don't understand mud. Also, I stopped betting on the horses after Dark Ivy died at the ludicrous Becher's Brook, but it seems horses can be killed just in the paddock by electricity in the ground www.express.co.uk/sport/horseracing/229623/Accidental-electrocution-blamed
Those WWI trench telephones with an earth return had a major downside. The Germans could sneak into no man's land, plant two ground rods, and sneak back with a cable to each. Often there was enough voltage induced between the two rods to give them a tap on that phone.
Old electricians trick to get the earth loop impedance to the required level is to dump a bucket of water on the electrode and then put the wet electrode readings down on the certificate.
@@r.h.8754 Thanks for info re permission and extra earthing arrangements for N. Totally agree on your points re N failure risks. Defective cherry picker. A burst hose should disable the machine, not let it drop. For that reason, they are power up and power down. (Unlike forklifts that use gravity to lower the forks.) Manual lowering systems can use gravity but to operate, a normal operation safety system needs to be bypassed and that function is usually spring-loaded so requires person in attendance at all times holding the bypass valve open.
Ha. Can you Imagine J.W On the Trampoline ? Bouncing up and Down haha Doing Twists and Turns and even Summer Salts ha ha ha.... He can connect his Earth Electrode to the Trampoline Body frame... ha ha ha
