Bdtjtk

var $select1 = $('#select1'),

  $select2 = $('#select2'),

  $select3 = $('#select3'),

  $options = $select2.find('option'),

  $options1 = $select3.find('option');



$select1.on('change', function() {

  $select2.html($options.filter('[value="' + this.value + '"]'));

}).trigger('change');

$select2.on('change', function() {

  $select3.html($options1.filter('[value="' + this.value + '"]'));

}).trigger('change');

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

<select name="select1" id="select1">

    <option value="1">Option 1</option>

    <option value="2">Option 2</option>

</select>



<select name="select2" id="select2">

    <option value="1">Option 1</option>

    <option value="1">Option 2</option>

    <option value="2">Option 1</option>

    <option value="2">Option 2</option>

</select>



<select name="select3" id="select3">

    <option value="1">Option 1.1</option>

    <option value="1">Option 1.2</option>

    <option value="2">Option 2.1</option>

    <option value="2">Option 2.2</option>

    <option value="3">Option 3.1</option>

    <option value="3">Option 3.2</option>

    <option value="4">Option 4.1</option>

    <option value="4">Option 4.2</option>

</select>

var $select1 = $('#select1');

var $select2 = $('#select2');

var $select3 = $('#select3');



$select1.on('change', function(){

  var chose = $(this).find(':selected').data('chose');

  console.log('chose 1:', chose);

  $select2.val(chose).trigger('change');

});



$select2.on('change', function(){

  var chose = $(this).find(':selected').data('chose');

  console.log('chose 2:', chose);

  $select3.val(chose).trigger('change');

});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>



<select name="select1" id="select1">

    <option data-chose="1" value="1">Zahle</option>

    <option data-chose="2" value="2">Other</option>

</select>



<select name="select2" id="select2">

    <option data-chose="1" value="1">1 Single Phase System</option>

    <option data-chose="1" value="2">2 Three Phase System</option>

    <option data-chose="2" value="3">3 Single Phase System</option>

    <option data-chose="2" value="4">4 Three Phase System</option>

</select>



<select name="select3" id="select3">

    <option data-chose="1" value="1">1 Flat1</option>

    <option data-chose="1" value="2">2 Pitched1</option>

    <option data-chose="2" value="3">3 Flat2</option>

    <option data-chose="2" value="4">4 Pitched2</option>

</select>

// Dom element to store clones in it

var $clones = $('<div/>');

// Clone all select elements

$('select').each(function(){

  $clones.append($(this).clone().attr('id', $(this).attr('id') + '-clone'));

});



// On a change remove the options that do not belong to the same value.

$('select[data-change]').on('change', function(){

	var $this = $(this);

  var selected = $this.val();

  var toChange = $this.data('change').split(',');

  for(id in toChange) {

    var toChangeId = '#' + toChange[id];

    var toChangeCloneId = toChangeId + '-clone';

    $(toChangeId).html($(toChangeCloneId, $clones).html());

    $(toChangeId).html($('option', toChangeId).filter('[value="' + selected + '"]'));

  }

});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

<select name="select1" id="select1" data-change="select2,select3">

    <option value="1">Zahle</option>

    <option value="2">Other</option>

</select>



<select name="select2" id="select2">

    <option value="1">Single Phase System</option>

    <option value="1">Three Phase System</option>

    <option value="2">Single Phase System</option>

    <option value="2">Three Phase System</option>

</select>



<select name="select3" id="select3">

    <option value="1">Flat1</option>

    <option value="1">Pitched1</option>

    <option value="2">Flat2</option>

    <option value="2">Pitched2</option>

</select>