effect of over rated fuse  - Page 1
Forum section: electronics / general

author: hussamaldean
author_rank: Unknown
timestamp: March 04, 2018, 04:48:51 pm
content: Hi all,I have uni-t multimeter and I burnt the mA range fuse by accident ( it was on mA range when I tried to measure voltage). however, the range is protected by FF 600mA fuse (unknown brand ) and I couldn't find this range so I used FF 1.6A from SIBA. the question is, what is the effect of such fuse on mA range measurement ?Regards

author: Neilm
author_rank: Super Contributor
timestamp: March 04, 2018, 05:56:17 pm
content: The next time you overload the mA range, a lot more power will get through before the fuse blows. Depending on the circuit, it may or may not be able to handle it. There is also the possiblility that you connect on and you have a reasonably large source impedance. This could mean that the fuse doesn't blow (a 2A overload would blow a 600mA in a second or so but it is unlikely a 1.6A fuse would blow), something gets very hot and the meter could catch fire.Most likely, the next time you overload it you will have to buy a new meter.

author: hussamaldean
author_rank: Unknown
timestamp: March 04, 2018, 06:21:11 pm
content: Quote from: Neilm on March 04, 2018, 05:56:17 pmit was 24V with current limiting of 1Athats all

author: Nusa
author_rank: Super Contributor
timestamp: March 04, 2018, 06:44:03 pm
content: To answer your original question directly, using the wrong fuse will have no effect on the meters ability to measure the proper range of current. The fuse is there solely to protect the meter from an improper amount of current. With the your current fuse, your next mistake will be likely be the last mistake for that meter....if you're lucky, you'll only lose the ma range, but expect to lose everything.

author: Zero999
author_rank: Super Contributor
timestamp: March 04, 2018, 07:13:51 pm
content: As mentioned above, the meter will still be fully functional, with a 1.6A fuse, rather than a 600mA fuse, but it's a bad idea, because you lose the protection.One thing to note is that, in resistive loads, such as cables and the meter's current sense resistor, the power dissipation increases to the square of current. The power dissipation inside the meter and cables will increase by a factor of 1.62/0.62= 7.11, when the current is increased from 0.6A to 1.6A. In reality, the short circuit current can be a thousand times those figures, causing a massive power dissipation, inside the meter, even with the 600mA fuse. If it's replaced with a 1.6A fuse and is overloaded, it may blow up. If the circuit has enough energy, this can cause serious injury or death to the person holding the meter.

author: tooki
author_rank: Super Contributor
timestamp: March 05, 2018, 12:45:45 am
content: Order a 600mA fuse. And if the original was a simple glass fuse, upgrade it to a ceramic fuse, or even a proper multimeter fuse if you can find one of the right value and dimensions.Also make sure to match trip speed of the fuse. If the meter was designed for 600mA fast blow, you do not want a 600mA slow blow because it will allow excess current for much longer, and may damage the meter.

author: hussamaldean
author_rank: Unknown
timestamp: March 06, 2018, 06:05:59 am
content: Quote from: tooki on March 05, 2018, 12:45:45 amIf I want to order from the internet, I have to wait like 2-months to arrive to Iraq (due to new tax laws) and I have to pay the shipping fees also

author: tooki
author_rank: Super Contributor
timestamp: March 06, 2018, 08:33:50 am
content: Quote from: hussamaldean on March 06, 2018, 06:05:59 amSo leave the incorrect fuse in for now, use the meter extra-carefully, while you wait for the correct fuse to arrive.

author: hussamaldean
author_rank: Unknown
timestamp: March 06, 2018, 08:34:50 am
content: Quote from: tooki on March 06, 2018, 08:33:50 amsoon I will get my hand on Gossenmetrahit Pro

author: tooki
author_rank: Super Contributor
timestamp: March 06, 2018, 03:32:59 pm
content: Very nice! Just make sure you don’t make the same mistake again, measuring volts in amps — the fuses in that caliber of multimeter are very expensive!Or wait, is the Metrahit the meter with automatic covers over the jacks as you turn the range switch??

author: hussamaldean
author_rank: Unknown
timestamp: March 06, 2018, 03:34:09 pm
content: Quote from: tooki on March 06, 2018, 03:32:59 pmyep

author: hussamaldean
author_rank: Unknown
timestamp: March 07, 2018, 01:07:59 pm
content: quick questionhow can I know if I bought original SIBA fuses ?