Touch current in single fault conditions test and earth leakage current in normal conditions test, are they really different tests?

#1
Hello everybody,
We were checking IEC 60601 third edition rule and we found some points we have questions about. We will explain them one by one:
This rule (IEC 60601 third edition) stablishes the following limit in section c). It establishes a 500 µA limit for TOUCH CURRENT in SINGLE FAULT CONDITIONS and a 5 mA limit in section d) for EARTH LEAKAGE CURRENT in NORMAL CONDITIONS. I have attached on a screenshot the corresponding imagen below:

1559830630302.png


So, if we look at TOUCH CURRENT in SINGLE FAULT CONDITIONS test explanation, the definition is the one remarked on blue:

1559830655436.png


By other hand, if we see EARTH LEAKAGE CURRENT in NORMAL CONDITIONS test explanation, the definition is:

1559830678694.png


So, our question is:
In a medical equipment class I with accessible conductive parts in the enclosure that are normally protectively earthed, are both tests equal but with different limits and if in EARTH LEAKAGE CURRENT in NORMAL CONDITIONS test we are not under 500 µA it is impossible to meet the limit of TOUCH CURRENT in SINGLE FAULT CONDITIONS?
Or, it is that TOUCH CURRENT in SINGLE FAULT CONDITIONS must be applied on conductive parts of the enclosure that are not protected grounded?

Any help with this issue would be grateful.
 
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Pads38

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#2
As this has not yet been picked up I shall try and help...

The tests you enquire about are quite separate and different tests. Perhaps the clearest way to see this is to examine Figures 13 and 14 and notice the different use of the Measuring Device (MD).

In figure 13, for Earth leakage, the MD is in the earth conductor so measures all currents. Figure 14 it is shown ending in an arrow - this is meant to indicate that it is a measuring probe, which is then used all over the enclosure. For plastic parts or enclosure it is used in conjunction with metal foil.

You will only get a reading for touch current of protectively earthed metal parts in the Single Fault Condition of the earth connection open, effectively when they are no longer protectively earthed.
 
#3
Hello!

First, thank you so much for your replay. But I still can´t understand completly the answer. I mean, according to Figure 14, in Single Fault Condition, if we messure with the MD between earth and all metalic parts that were connected to earth, but now not for the SFC, we are meassuring exaclty as in Figure 13 where all parts are earth connected.

The point is that the limit of touch current in Single Faut Conditions is well bellow the limit of earth leakage and MD is the same one and the test is also the same one so, we understand that, if Single Fault Conditions Touch Current limits are not met, it seems impossible to meet the test.

Thank you in advance. It is quite complex
 
#4
Hi Alba,

Fig. 14 in SFC with Protective Earth open would be the same as Fig 13. in NC if we measured Touch Current in an enclosure connected to Protective Earth.

However, a key point to consider is that you shall measure Touch Current for parts that are not protectively earthed. You don't measure TC on earthed enclosures.

I hope this helps to clarify.
 
#5
Hi everybody,

First, thank you so much for your answers, there are being so usefull!

Regarding to the last replay, I think there is something that I am missing because, if you look at one of the first images I posted (I attach it in this post too), concretly imagen with point 8.7.4.6, you will see remarked in blue a quote when it is said that TC can be messured in a Protectively Earthed part in SFC.

So, in this case, Fig. 14 ans Fig 13. would be the same.
 

Pads38

Trusted Information Resource
#6
Touch Current can be Measured in a part that is Protectively Earthed - but only in the SFC of Earth Open.
Then it is, effectively, a conductive part that is NOT Protectively Earthed.
 
#7
Thank you so much for your answers. So, after your replay, I understand this confirm what we said that is:

if in EARTH LEAKAGE CURRENT in NORMAL CONDITIONS test we are not under 500 µA it is impossible to meet the limit of TOUCH CURRENT in SINGLE FAULT CONDITIONS in a part that is Protectively Earthed but in the SFC of Earth Open this conductive part is NOT Protectively Earthed.

Right?
 

Kuldeep Singh

Involved In Discussions
#8
Hi everyone,

We are manufacture of X-Ray medical products and perform different tests as per IEC 60601-1 in our internal lab.

We have Leakage current tester (Hioki Make) for single phase machine and able to perform leakage current tests on single phase machine easily. But we face difficulties in three phase machine. Is it applicable to three phase machine ? because it is a difficult task to create single fault condition in three phase machine.

Is there any Leakage current tester for three phase ?
 
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