Measuring mains current - Page 1
Forum section: electronics / beginners

author: miketan3904
author_rank: Contributor
timestamp: June 18, 2020, 06:48:25 am
content: Hi! I'm using the ACS712 current sensor to measure the mains current. I would like to ask whether it's safer to measure the current at live or neutral. Thanks.

author: 0culus
author_rank: Super Contributor
timestamp: June 18, 2020, 07:05:36 am
content: For mains? I'm not familiar with the device you mention, and you didn't mention the application, but I'd use a clamp meter for that. Much safer than breaking the circuit and putting something in series.

author: miketan3904
author_rank: Contributor
timestamp: June 18, 2020, 07:16:48 am
content: I'm trying to build a device to measure the power of home appliances. The mentioned sensor will be used to measure the current for power calculation.Here's the picture of the sensor:

author: 0culus
author_rank: Super Contributor
timestamp: June 18, 2020, 07:20:56 am
content: That thing looks kinda dangerous to me. Is it really intended for mains use? Remember, you aren't playing with a low energy 5V circuit anymore here. Mains can dump huge amounts of energy if something goes wrong.Why not just buy a Kill-a-Watt?

author: Ian.M
author_rank: Super Contributor
timestamp: June 18, 2020, 07:31:02 am
content: Both the Line and Neutral conductors must always be regarded as live from a safety point of view, as a loose neutral connection anywhere 'upstream' in the supply could result in the whole supply voltage appearing on the neutral conductor via connected loads. Also, in many parts of the world, domestic mains connectors are not reliably polarised, so Line and Neutral are effectively interchangeable.Therefore it comes down to whether or not an ACS712 (as installed on your PCB) can meet the creepage and clearance distance and isolation voltage requirements for themeasurement categoryappropriate to your device's intended usage.For the complete sensor you've shown, you'd need to have obtained it from a supplier that could guarantee full supply chain traceability to ensure the ACS712 is genuine, assess its PCB layout to check creepage and clearance distances, and also develop a safe and reliable way to mount it.As the ACS712 has been discontinued for several years, the odds of it being traceably genuine are poor,

author: Alti
author_rank: Frequent Contributor
timestamp: June 18, 2020, 08:06:22 am
content: Pictured module is not intended for mains voltages. It has a GND pour all over the board and clearance in the order of 0.5mm so this defies the 2100V isolation of the chip itself.Keep in mind that mains installations are protected by circuit breakers/fuses and have short-circiut ratings counted in "prearcing i2t" (unit is A2s). The ACS modules have ratings in 100ms pulses. In case of any shorts, depending on your skills, this design is either going to be a current sensor protecting the fuse or the fuse protecting current sensor.

author: Vovk_Z
author_rank: Super Contributor
timestamp: June 18, 2020, 05:36:37 pm
content: Quote from: miketan3904 on June 18, 2020, 06:48:25 amIn general we (may pretend that) don't know exact witch wire is live and whitch is neutral (for home/office use devices). So it is the same.If a mains connector and the whole mains network is such designed so we definitely know which wire is live (it is usually in industry) - then of cause neutral is safer.

author: TimFox
author_rank: Super Contributor
timestamp: June 18, 2020, 06:14:33 pm
content: Suitable current transformers, with a large enough hole to clear a well-insulated mains wire, are readily available. They need to be terminated with an appropriate resistor (see data sheet) so that an AC voltmeter can read the current. The insulation on the wire provides sufficient isolation for safe measurement.Here are some from Triad Magnetics for 50/60 Hz operation.https://www.mouser.com/Power/Transformers/Current-Transformers/_/N-8u9qqZ1yzvvqx?P=1yuv0v4Z1z0z63x