By how the current changes during these 1000 seconds. In the case of copper wire, it will hardly change. 

To kolbacict.
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Good question! And here is the answer. Actually two answers.
1) Regularly cooling down the electrolyzer by some cooling agent, which can be for example the water used in your hot-water heating system.
2) The period of time is not necessary to be equal to 1000 seconds. The period of time could be equal to 100 seconds, 10 seconds or even 1 second. The electrlyte's Ohmic resistance will not change and will remain practically constant within a period of 10 seconds for example. 

Let us focus again on pure theory. 
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Please have a look again at our post of October 31, 2020, 10:07:39 AM. For your convenience I am giving below the text of this post. (The text is surrounded/limited up and down by double dashed lines.)
===============================
Here is a continuation/variation of our previous post of October 18, 2020, 05:28:00. (Please look at besslerwheel.com/forum. Almost the same text in the related topic of the same title.)
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1) Let us assume again that the energy consumed by the standard water-splitting electrolyzer is just equal to the sum of (a) the Joule's heat and (b) the heat, generated by the burning/exploding of the released hydrogen. Therefore we can write down the equality
V x I x t = (I x I x R x t) + (Z x I x t x (HHV)) (1)
where
V = DC source voltage
I = DC current
R = Ohmic resistance
t = time
Z = electrochemical equivalent of hydrogen
HHV = higher heating value of hydrogen
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2) Let us decrease n times voltage V, that is,
V x I x t = (I x I x R x t) + (Z x I x t x (HHV)) (1) <=>
<=> (V/n) x (I/n) x t < ((I/n) x (I/n) x R x t) + (Z x (I/n) x t x (HHV)) (2)
where
n > 1
R = const.; for how to keep R constant please refer for example to our post of July 04, 2020, 01:38:09.
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3) Now let us increase n times voltage V, that is,
V x I x t = (I x I x R x t) + (Z x I x t x (HHV)) (1) <=>
<=> (nV) x (nI) x t > ((nI) x (nI) x R x t) + (Z x (nI) x t x (HHV)) (3)
where
n > 1
R = const.; for how to keep R constant please refer for example to our post of July 04, 2020, 01:38:09.
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4) In one word, it is evident that:
a) equality (1) shows that efficiency is equal to 1;
b) inequality (2) shows that efficiency is bigger than 1;
c) inequality (3) shows that efficiency is smaller than 1.
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5) Therefore by regulating the value of V we can regulate and control the value of efficiency. In other words, efficiency can be either (a) bigger than 1 or (b) equal to 1 or (c) smaller than 1. And this depends on the value of V.
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6) let us remind again that in order to be more precise we have to use V - v instead of V and I - i instead of I, respectively. (For v and i please refer to our previous post of October 18, 2020, 05:28:00.) But if V (and V/n too!) is much bigger than v (and I (and I/n too!) much bigger than i, respectively), then v and i can be neglected and therefore (1), (2) and (3) are perfectly correct.
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7) In one word, we proved theoretically again that the law of conservation of energy is not always valid for any standard DC water-splitting electrolysis process.
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Do you have any theoretical (ONLY THEORETICAL!) objections against the text above? Is there any formula/logical construction in the text above which is incorrect and if yes, then why? Please focus solely and only on the analysis (line by line) of the text above.
================================
Looking forward to your answer.
George1
Looking forward to your answer.
George1

A hot discussion occurs in besslerwheel.com/forum. The title of the topic is just the same.
I am giving below again the text of our last post of October 18, 2020, 08:15:09 PM. The post's text is surrounded/limited up and down by double dashed lines.
====================
Let us assume that the energy consumed by the standard water-splitting electrolyzer is just equal to the sum of (a) the Joule's heat and (b) the heat, generated by the burning/exploding of the released hydrogen. Therefore we can write down the equality
V x I x t = (I x I x R x t) + (Z x I x t x (HHV)) (1)
where
V = DC source voltage
I = DC current
R = Ohmic resistance
t = time
Z = electrochemical equivalent of hydrogen
HHV = higher heating value of hydrogen
Therefore we can write down the inequalities
V x I x t > I x I x R x t (2) <=> V > I x R (3) <=> V/R > I (4).
-----------------------
The last inequality (4) unambiguously shows that Ohm's law is not valid for liquid resistors.
----------------------
The above considerations are not very precise however. In order to be precise enough we have to introduce the quantities v an i. In other words, we must write down the equality
(V - v) x (I - i) x t = ((I - i) x (I - i) x R x t)+(Z x (I - i) x t x (HHV)) (5)
where
V = DC source voltage
I = DC current
R = Ohmic resistance
t = time
Z = electrochemical equivalent of hydrogen
HHV = higher heating value of hydrogen
v = minimum voltage necessary for the water-splitting electrolysis to begin
i = the related small decreasing of current I, caused by the presence of v.
And from here we can write down the inequalities
(V - v) x (I - i) x t > (I - i) x (I - i) x R x t (6) <=>
<=> V - v > (I -i) x R (7) <=> (V - v)/R > I - i (.
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The last inequality ( shows again that Ohm's law is not valid for liquid resistors.
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It is evident that if V is much bigger than v (and I much bigger than i, respectively), then v and i can be neglected and in this case inequality ( can be replaced with inequality (4).
In one word, if equalities (1) and (5) are valid, then inequalities (4) and ( are valid too. But this means that Ohm's law is not valid for liquid resistors.
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Ohm's law is the most basic and most fundamental axiom of electric engineering. No Ohm's law -- no electric engineering.
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Looking forward to your answer.

Number eight in brackets is replaced by some stupid head with black spectacles. Some error of the system.