Conductor Clearance: Voltage Difference Tab

The Voltage Difference sub-tab in the Conductor Clearance tab of the Rule Editor dialog allows you to set clearances between conductors that are within a specified voltage range. Using the Design Rule tab in Constraint Browser, you can override the default values specified for E-Nets in this dialog. Clearance values are checked using the Creepage Check command. The results are displayed in the Creepage Check Results dialog.

Item		Description
Clearance Priority		Allows you to select how the effective value for conductor clearance is set. This can be set by searching a hierarchical list of clearance values. Clearance rules that are set in the Conductor Clearance: Voltage Difference Tab, Constraint Browser or the Default Design Rule Stack section in Rule Editor are followed, in the hierarchical order shown below. Alternatively, you can use the largest clearance value that is specified in either Constraint Browser or Rule Editor.
	Use hierarchy	The effective value for conductor clearance is set by checking clearance rules in the following order. The first clearance value that is found is used. Click the relevant row in the following image for a description of where the value is set. Further information regarding the clearance rules is provided in the Note section below. Note Item 1: if a voltage is set against a Net, then clearances are checked using the difference between the voltages of the nets. This is defined in the Voltage difference clearance table, in the Conductor Clearance: Voltage Difference Tab in Rule Editor. If Nets do not have a voltage defined, then the voltage difference is set in the Default Attributes for Signal section. Item 2: clearance values are used that are set in the Rule Area Attributes dialog for the Net. Items 3 to 8: if a voltage is set against a Net and a table stack is also set against a Net in the Design Rule tab in Constraint Browser, then the specified table stack is used as the clearance. Item 9: if no voltage or clearance stack is set for a Net, then the Default design rule stack determines the clearances.
	Use largest value	The largest clearance value is used that is set in either the Design Rule sub-tab, Voltage Difference Clearance section in Constraint Browser, or in the Default design rule stack section in Rule Editor. In the following example, a clearance of 0.1 mm is set in the Default design rule stack, and a clearance formula of 0.00305 * Vdiff + 0.05000 is specified in the Clearance dialog. Below approximately 16V, the clearance is defined by the Default design rule stack. Above this voltage, the clearance is defined by the formula as this produces the largest clearance values.

Item

Description

Clearance Priority

Allows you to select how the effective value for conductor clearance is set. This can be set by searching a hierarchical list of clearance values. Clearance rules that are set in the Conductor Clearance: Voltage Difference Tab, Constraint Browser or the Default Design Rule Stack section in Rule Editor are followed, in the hierarchical order shown below. Alternatively, you can use the largest clearance value that is specified in either Constraint Browser or Rule Editor.

Use hierarchy

The effective value for conductor clearance is set by checking clearance rules in the following order. The first clearance value that is found is used. Click the relevant row in the following image for a description of where the value is set. Further information regarding the clearance rules is provided in the Note section below.

Note

Item 1: if a voltage is set against a Net, then clearances are checked using the difference between the voltages of the nets. This is defined in the Voltage difference clearance table, in the Conductor Clearance: Voltage Difference Tab in Rule Editor. If Nets do not have a voltage defined, then the voltage difference is set in the Default Attributes for Signal section.
Item 2: clearance values are used that are set in the Rule Area Attributes dialog for the Net.
Items 3 to 8: if a voltage is set against a Net and a table stack is also set against a Net in the Design Rule tab in Constraint Browser, then the specified table stack is used as the clearance.
Item 9: if no voltage or clearance stack is set for a Net, then the Default design rule stack determines the clearances.

Use largest value

The largest clearance value is used that is set in either the Design Rule sub-tab, Voltage Difference Clearance section in Constraint Browser, or in the Default design rule stack section in Rule Editor. In the following example, a clearance of 0.1 mm is set in the Default design rule stack, and a clearance formula of 0.00305 * Vdiff + 0.05000 is specified in the Clearance dialog.

Below approximately 16V, the clearance is defined by the Default design rule stack. Above this voltage, the clearance is defined by the formula as this produces the largest clearance values.

Default attributes for signal

Sets default voltages for Nets that have no voltage defined in Constraint Browser.

Note
When the voltage difference between conductors is calculated using the Creepage Check Results dialog, the Creepage results are affected by the voltage attributes below.

If a Phase Group value is not set for both nets, or is different.
For each net, the Low Voltage value of one net is compared with the High Voltage value of the other net.
For each net, the High Voltage value of one net is compared with the Low Voltage value of the other net.

The largest difference is set as the Voltage difference value in the Creepage Check Results dialog.

If the same Phase Group value is set for both nets.
The Voltage, Low Voltage and High Voltage values are compared between each net. The largest difference is set as the Voltage difference value in the Creepage Check Results dialog.
If Low Voltage or High Voltage values are not set, then the Voltage value is used instead. The Voltage, Low Voltage and High Voltage values are then compared between each net. The largest difference is set as the Voltage difference value in the Creepage Check Results dialog.
If only Low Voltage or High Voltage values are set for a particular net, then these values are used for the missing Voltage, Low Voltage or High Voltage values. The Voltage, Low Voltage and High Voltage values are then compared between each net. The largest difference is set as the Voltage difference value in the Creepage Check Results dialog.

Item	Description
Voltage [V]	The default voltage value of a signal. For a signal that is displayed in the Creepage Check Results dialog, this value is displayed, by default, if a voltage value is not specified for it. The above Note describes how this value is used in the Creepage Check Results dialog if a Voltage value is not defined in Constraint Browser.
Minimum voltage [V]	The most negative voltage a signal can carry. For a signal that is displayed in the Creepage Check Results dialog, this value is displayed, by default, if a minimum voltage value is not specified for it. The above Note describes how this value is used in the Creepage Check Results dialog if a Low Voltage value is not defined in Constraint Browser.
Maximum voltage [V]	The most positive voltage a signal can carry. For a signal that is displayed in the Creepage Check Results dialog, this value is displayed, by default, if a maximum voltage value is not specified for it. The above Note describes how this value is used in the Creepage Check Results dialog if a High Voltage value is not defined in Constraint Browser.
Phase group	Phase groups allow you to group elements, and can be used as follows to change how the results are calculated. They are specified in the Design Rule tab in the Constraint Browser: Signals section, Signals tab. When the voltage difference between conductors is calculated, the Phase group value is used as follows. If the phase group names are not specified or are different between two signals: the voltage differences are calculated for all combinations of the highest voltages and lowest voltages (or voltages if they are not set) set for the two signals, and the maximum voltage difference among them is applied. If the voltage is not set for a signal, then the voltage set as a default attribute for the signal is referenced. If two signals have the same phase group name: the voltage differences are calculated between the highest voltages, between the lowest voltages (or if they are not set, between voltages) for the two signals. The maximum voltage difference among them is applied. If the voltage is not set for a signal, then the voltage set as a default attribute for the signal is referenced. See the above Note for further details on how the Phase group value is used in the Creepage Check Results dialog.

Active clearance table stack for board

Allows you to assign the voltage difference clearance table stacks that you create in the Voltage difference clearance table stack section. If specified, then this clearance is referenced, by default, by the Creepage Check command. You can set default clearances for nets that have voltages defined or undefined.

Item	Description
Between voltage defined net and undefined	Specify the voltage difference clearance table stacks that are referred to by the Creepage Check command for clearances between nets whose voltage is defined, and those whose voltage is undefined. These clearance table stacks are created in the Voltage difference clearance table stack section.
Between voltage defined nets	Specify the voltage difference clearance table stacks that are referred to by the Creepage Check command for clearances between nets whose voltage is defined. These clearance table stacks are created in the Voltage difference clearance table stack section.

Voltage difference clearance table stack

Allows you to specify the clearance value that is applied to each conductor, for particular voltage ranges. Clearance values are set in the voltage difference clearance table that you select. These must be created previously in the Voltage difference clearance table section.

Note
You can import a Voltage difference clearance table stack from the design rule library using the Import Design Rule Library (Partial) dialog.

Item		Description
Voltage difference clearance table stack box		Define the alphanumeric name of a voltage difference clearance table stack, and press Return or click Add. It is created, and added to the Voltage difference clearance table stack list.
Add		Adds the voltage difference clearance table stack that you define to the Voltage difference clearance table stack list. Alternatively, press Return.
Voltage difference clearance table stack list		Displays the voltage difference clearance table stacks that you create using the Voltage difference clearance table stack box. Click an item to display it in the Conductor table. Note Right-clicking an item allows you to delete or duplicate it. If you duplicate an item, specify its name in the displayed Duplicate dialog.
Conductor table		For the item that you click in the Voltage difference clearance table stack list, specify a voltage difference clearance table for each conductor layer by selecting it in the relevant drop down list. These must be created previously in the Voltage difference clearance table.
	Conductor layer	Displays the conductor layers for which voltage difference clearance tables can be selected.
	Clearance table	For each conductor layer, specify a voltage difference clearance table by selecting it in the associated drop down list.

Voltage difference clearance table

Allows you to specify the clearance value that is applied when the voltage difference between conductors is within the appropriate range. If you specify values in this section, then a voltage difference above a defined threshold can be assigned a particular clearance value, and a voltage difference below the threshold can be assigned a different clearance value.

You can define clearances using either a clearance rule or formula. When clearance items are set, the Clearance/Voltage graph is populated. This shows the clearance values for each voltage difference range.

Note
You can import a Voltage difference clearance table from the design rule library using the Import Design Rule Library (Partial) dialog.

Item		Description
Voltage difference clearance table name box		Define the alphanumeric name of a voltage difference clearance table, and press Return or click Add. It is created, and added to the Voltage difference clearance table name list.
Add		Adds the voltage difference clearance table name that you define to the Voltage difference clearance table list. Alternatively, press Return.
Voltage difference clearance table name list		Displays the voltage difference clearance table names that you create using the Voltage difference clearance table name box. Click an item to display it in the Voltage difference clearance table. Note Right-clicking an item allows you to delete or duplicate it. If you duplicate an item, specify its name in the displayed Duplicate dialog. You can select multiple items by dragging the cursor. Alternatively, use the Ctrl or Shift keys.
New threshold box		Define a numeric boundary value for a voltage range. This determines the point where the clearance value changes. Press Return or click Add to add it to the Voltage difference clearance table. For the first boundary value that you specify, two rows are created in the Voltage difference clearance table. First row: specify a clearance from 0 volts to the specified value. Second row: specify a clearance for voltages that are greater than the specified value. For each row, point the cursor in the Clearance column and click to select a clearance in the displayed Clearance dialog.
Add button		The boundary value that you define is added to the Voltage difference clearance table. Alternatively, press Return. Values are listed in the table in order of voltage.
Voltage difference clearance table		The boundary values that you specify in the New threshold box are listed in order of voltage. For each row, point the cursor in the Clearance column and click to select a clearance in the displayed Clearance dialog. When clearance items are set, the Clearance/Voltage graph is populated. This shows the clearance values for each voltage difference range. Note Delete a row by right-clicking it, and clicking Delete Selected Rows on the assist menu. Delete multiple rows by dragging the cursor to select them. Alternatively, use the Ctrl or Shift keys.
	Voltage difference [V]	>=Minimum: displays the lower value of the voltage difference. This value is added automatically to the Voltage difference clearance table when you add a boundary value using the New threshold box. <Maximum: displays the upper value of the voltage difference. This value is added automatically to the Voltage difference clearance table when you add a boundary value in the New threshold box.
	Clearance	Allows you to specify a clearance value for each voltage range. Either type in a value, or point the cursor in the Clearance column and click to select a clearance in the displayed Clearance dialog. These clearances are set in the Design rule group section of the Conductor sub-tab, in the Conductor Clearance tab of the Rule Editor dialog. The contents of the row are immediately represented in the Clearance/Voltage graph. Note If you specify a formula for the clearance using the Formula tab in the Clearance dialog, then this is displayed in the Clearance column, rather than a clearance value.
Clearance/Voltage graph		The clearance values for each voltage difference range in the Voltage difference clearance table are displayed graphically. These are displayed automatically when you add values in this table. Specify a clearance value for each row using the Clearance dialog.

Related Topics
Clearance
Rule Editor Dialog
Creepage Check
Creepage Check Results
Understanding Creepage